I've made this galette using Fontina.

https://smittenkitchen.com/2007/10/butternut-squash-and-caramelized-onion-galette/

Gruyere would be my choice too.

Thanks all. I'll go with Gruyere.

I hate saying this as I am a good cheese lover, but gruyere is one where I often like swiss better.

I used to be able to buy a Brie that was smothered in caramelized onions and mushrooms, then wrapped in pastry.... Yum.

PM just got me thinking of cambozola. That might get pretty rich but sounds good to me.

A mild Gouda sounds good too.

Goat cheese and caramelized onions - a nice sweet-savory taste.

Blue cheese and caramelised onion tart used to sell well at a restaurant where I worked back in the day.

Well, now, lots of good ideas!

Cheddar or Beemster might be good too...

Hmmm. I know cheddar of course, but what is Beemster?

I can't think of any cheese that wouldn't go well with caramelized onions....
Parm is also good.....the strong taste balances well with the onions....as does Peccorino Romano.

What about a good Havarti?

Pecorino Romano is my favorite cheese. I would love the salty sweet taste of that with the onions.

https://beemstercheese.us/

Goat cheese is a popular combination (with fresh thyme), as is Gruyere. You could also add creme fraiche and bacon to the base and make a tarte flambee/flammkuchen.

Well, this is going to be one of the vegetarian choices, so no bacon.

So you're taking naan, then topping it with cheese and c. onions? then heating it? wondering what you're going for....

If you are using naan, then a really melty cheese would be good - kind of like a pizza type hors d'oeuvre. I would use gruyere or a mozzarella type cheese and add some garlic and sauted mushrooms.

I top naan all the time with all sorts of cheeses but asiago is my favorite mixed with a melty cheese, usually fresh mozzarella.

I'm planning on 4 different toppings--a cold one spread with drained yogurt mixed with lemon zest and topped with smoked salmon, marinated artichoke hearts and scallions or red onion (have made this for myself and it was delish); one with mozzarella and (locally raised) Italian sausage; one with whatever cheese and caramelized onions, and one with mozzarella and my home made pancetta (from locally raised, grass fed pigs). Probably will add some asiago or parmesan to that one or the sausage one. All except the first will be heated to melt the cheeses.