In a mixing bowl, combine the grated or finely chopped cheeses, diced tomatoes, finely sliced onions, and spices. Add the bacon bits if desired, then mix everything together until the filling is well combined.
Spread a thin layer of butter on one side of each tortilla. Spread the mixture evenly over half of the unbuttered side, making sure it's well distributed, then fold the other half over to close it.
Place the filled tortillas on a baking sheet. Bake for 5 minutes, gently flip them over, then continue baking for another 5 minutes until they are crispy and golden brown.
Remove the quesadillas from the oven, cut them into portions, and serve immediately.
