Preheat your oven to 400F and move the rack to the top third of the oven.
Melt the butter in a large, oven safe skillet over medium heat. Sauté the onions until softened and lightly browned (about 7-10 minutes).
Add the green chilies, enchilada sauce, chicken broth, sour cream, chili powder, garlic powder, onion powder, smoked paprika, cumin, and oregano, and stir until smooth.
Stir in the chicken and 1/2 cup of the cheese. Turn the burner off.
Add in the tortillas and toss gently until they're folded in (I find it easiest to do this with two spoons), and ensure they're well coated and spread out around the skillet fairly evenly.
Top with the remaining cheese and bake for 15 minutes or until hot and bubbly. Broil for a few minutes to brown the cheese more if needed (watch it doesn't burn).
Let it sit for a few minutes and season with salt & pepper as needed. Serve with sour cream, chopped cilantro, avocado, and jalapeno peppers if desired. I use a spatula to cut it into slices.