Roughly 25 years ago, Rita Wilson went to see a one-woman show in Los Angeles called “My Big Fat Greek Wedding.”

“The title made me laugh,” she recalls. “It was so great, and I thought, ‘This could actually be a fantastic movie.’”

So, along with husband Tom Hanks, Wilson signed on as a producer and helped bring Nia Vardalos’ heartwarming comedy to the big screen. Like the play, the 2002 film follows a young Greek-American woman named Toula (Vardalos) who struggles to get her eccentric family to accept her non-Greek fiancé (John Corbett). The movie became a staggering sleeper hit, raking in $369 million worldwide on a mere $5 million budget. It earned an Oscar nomination for best original screenplay and still remains the highest grossing rom-com ever.

It also spawned two film sequels, the latest being “My Big Fat Greek Wedding 3” (now in theaters), which finds Toula heading to the homeland for a family reunion with her daughter (Elena Kampouris).

The franchise is personal to Wilson, 66, who is part Greek and has Greek citizenship. She dyes eggs red for Greek Orthodox Easter, and even has her own “cheat” recipe for a quick tiropita, a layered phyllo and feta cheese pastry. (“I do a version with flour tortillas,” she says with a laugh. “They’re really good, and in a fix, it's a tiropita.")

Wilson, a prolific actress and singer, co-wrote the new film's end-credits theme “Oli Mazi (We Are All Together)” with Diane Warren. The joyous dance anthem features vocals by Wilson and singer Christos Mastoras, and has also been remixed by Dimitri Vegas and Like Mike. She tells us about the song and more.

More:At 61, Meg Ryan is the lead in a new rom-com. That shouldn’t be such a rare thing.

Question: How did “Oli Mazi” come about?

Rita Wilson: Nia was very specific about the kind of song she wanted. All the songs on the soundtrack are Greek, so she wanted a song that felt like it could be played in Greece or played in America. It's fun writing for a movie, because you get to take on these characters, in a way. It's like, "OK, what do we want to say so this song actually feels like it's part of the story?" It's a connective tissue.

I approached Diane to write it with me because of our friendship, and also her friendship with Nia. I had these words in my head, oli mazi – "we're all together" – because that's really what the film is about. Whether it's your own family or your chosen family of friends, you want to feel that everyone is there for you. It was really a celebration of the love that people bring to each other.

The original “Greek Wedding” is considered one of the most profitable movies of all time, making more than 70 times its budget. Was there a moment when you realized just how big it had become?

We never had expectations it was going to be a phenomenon. We just thought, “This is a pretty fun movie. I think people will like it.” It started as a very slow build. We kept making money and kept adding theaters, so it was really a word-of-mouth thing. We were never No. 1 (at the box office) – we were always No. 2 during those months. But when we finally got on “Oprah,” that's when we were like, “OK, this is a moment.”

I read that Nia promoted her one-woman show at Greek Orthodox churches. Did you use any similar grassroots marketing for the film?

Absolutely. We reached out to churches and said, “Please support this amazing movie about Greeks and family. If you feel like putting these flyers out, putting them in your church bulletins and telling people about the movie, that would be great.” And the Greeks showed up for us. But I also think people saw their own families in this Greek family. Even though you might have been Italian or Spanish or Indian, you thought, “Oh, I know this.” It's really about when you marry outside of your culture, what is that like?

Is it bittersweet to celebrate this film without Nia and the cast? (Vardalos directed, wrote and starred in “Greek Wedding 3,” but is not promoting it due to the ongoing actors’ and writers’ strikes.)

It really is, but we are all unified and very supportive of the strike. When you make a movie, you want it to culminate in a great celebration. There is no premiere, so we can't go to that. But there's greater issues at hand, so we're accepting of it.

Could there be a fourth movie at some point?

I think there's something to be said for a trilogy. Maybe there's something down the line – 10 years from now – where the kids are all grown, and John and Nia are grandparents. I’d like to see that; anything is possible.

I love your commitment to making projects set in Greece. (In addition to “Greek Wedding,” Wilson is also a producer of the “Mamma Mia!” franchise.)

It's so much fun. If I could have a mission statement about the kind of projects I want to be involved in, it's projects that bring joy to people. I was thinking the other day, “I wish there were more comedies out!” There are not enough. I remember when “Ticket to Paradise” came out (last year), I was so excited to see that movie, because I was just like, “Oh my god, there hasn't been a romantic comedy in (years). And now we have George (Clooney) and Julia (Roberts) together again.” So I'm voting for more comedies. I want more.