Heat the oven to 375 degrees. Grease a 9-by-13-inch casserole dish with oil or oil spray.
In a large bowl mix the chicken/beans, veggies, salt, garlic powder, chili powder, 1/3 cup salsa, and 1 1/2 cups shredded cheese. If using beans, I like to roughly mash them with a fork as I mix everything together.
Whisk together the remaining 1 cup of salsa with the greek yogurt. (I like to do this is a liquid measuring cup so it's easy to pour.) Pour half of the sauce into the bottom of your casserole dish and spread into an even layer.
Wrap the tortillas in a damp paper towel and heat in the microwave for 1 minute. (If you don't have a microwave, you can wrap the tortilla in foil and put them I the oven for 5 minutes.) This helps soften the tortillas so they are easy to roll.
Place one tortilla on your work surface/cutting board then add heaping spoonful of the filling evenly across the bottom third. Roll the tortilla around the filling then place seam-side down in the casserole dish. Repeat with the remaining tortillas and filling.
Pour the remaining sauce evenly over the top, spreading it around with the back of a spoon if needed. Sprinkle the remaining cheese over the top.
Bake until the sauce is bubbling and the cheese on top is browned in places, 15 to 20 minutes. Serve warm with toppings of your choice.
Leftovers can be refrigerated and reheated for 3 days. The casserole can be assembled up to a few hours ahead of time and then baked. The baked casserole can well wrapped and frozen for up to a month.