Preheat the oven to 425°F (220°C).
Heat 1 tablespoon oil in a large oven-proof skillet over medium-high heat.
Add the diced onion and cook, stirring occasionally, until tender, about 3–5 minutes.
Reduce heat to medium-low and add 3 cups shredded chicken; season with 1 teaspoon chili powder, 3/4 teaspoon ground cumin, 1/2 teaspoon smoked paprika, and salt and pepper to taste. Stir to combine.
Stir in the 4 oz can diced green chiles and 2 1/2 cups enchilada sauce until the chicken is evenly coated.
Add the 6-inch corn tortilla strips and toss or stir so they are fully coated in sauce; cook on low for about 2 minutes to soften the tortillas.
Evenly sprinkle 2 cups shredded cheese over the top of the skillet mixture.
Transfer the skillet to the preheated oven and bake 7–10 minutes until the cheese is melted; optionally broil for 1 minute to brown the cheese, watching carefully.
Remove from oven and let rest for 5 minutes, then top with desired optional toppings and serve warm.