Preheat the oven's broiler on a lower setting if available.
Heat oil in a deep oven-proof skillet over medium-high heat. Add onions and cook until softened, about 2 minutes.
Stir in beans, corn, and chicken until well combined and cook until heated through, about 5 minutes.
Pour over half of the enchilada sauce and top with half of the chips. Top with remaining sauce, remaining chips, and shredded cheese.
Remove from heat and transfer pan to the preheated oven on the middle rack. Bake until cheese is melted and bubbly, about 3 minutes.
Serve topped with desired toppings.
