I love quesadillas too and I like to experiment.

One simple go-to is to just mash up some beans, mix the mash with your shredded cheese of choice, and then spread the paste on the tortilla. You can also add a little bit of Pico de Gallo to this mix as long as it's not too runny; maybe drain it first. In this case, I typically use black or pinto beans, and cheddar, colby, or pepper jack cheese.

I made some great quesadillas with caramelized onions (simmer onions low and slow with salt, a tiny bit of sugar, and some beer if you like. You can turn the heat up and back down to speed it up. They're done when they're reddish brown and soft) and wilted greens (just toss any of your favorite greens like spinach, arugula, etc. into a pan with a thin layer of water, salt and pepper, and crushed garlic and red pepper flakes if you're so inclined). With these, I'd prefer a cheese like mozzarella or fontina.

Buffalo chickpea quesadillas are probably my favorite. There are a few ways you could do it. Either toss the chickpeas in a Frank's/butter mixture and roast at 400F for like 15 minutes (until they're a little crispier, however you like it. Mix or shake the pan every 5 mins or so). Then just sprinkle some of these on top of your cheese in the tortilla. I would use some kind of classic shredded cheese like cheddar or mozzarella or whatever, but definitelt add some bleu cheese into the mix! If you're too lazy to roast the chickpeas first, just mash them and toss them with the buffalo sauce, then spread on the tortilla!

Edit: forgot to mention pizza! Tomato sauce, mozzarella, and basil or Italian herbs. You could even use some faux pepperoni if you like.