So for the reset of your life you only can eat one type of ethnic food. Nothing else ever again. If you chose Portuguese, you have to eat Portuguese food for breakfast, lunch and dinner for the rest of your life.
Give me your top choices.
I’d probably go with Japanese first, then Italian. Enough variety to not get too terribly stale.
I’d go Greek! 
I take it that American is not an option?
Then I’d go with French. In very tiny portions.
Japanese.
Good loophole. Same for English.
Italian
Mexican
I’m going with Italian for my 1st choice. But Indian food is a close second. Yum!
Japanese. I couldn’t give up sushi.
Italian, then Indian. Whichever it was I would really, really miss the other.
I’d say Italian or Indian in that order as well.
Mexican by a wide margin.
French. Zero hesitation when I say that.
Korean.
Have to say Mexican - don’t know which I like better, the cheap stuff or the fancy stuff. It’s all good.
Moving thread from IMHO to Cafe Society.
American. If that is verboten, then Mexican, followed by Italian, Chinese and French.
Spanish. Second option, Italian. While I’ve only tried a couple of Israeli dishes, I’m reasonably sure I could survive on that too.
Saying “Chinese” or “Indian” seems like it’s as big a cheat as saying “Spanish”, mind you. They’re all wide enough that if you get bored it’s your fault.
Continental. I sure would miss all the other stuff though.
Indian! I love Italian as well, but I don’t think I could abstain from curries or masala chai without becoming severely depressed.
Italian and Mexican all the way. Last on my list Chinese.