Prepare the Chicken: Heat 1 tbsp olive oil in a large skillet over medium-high heat. Season chicken breasts with chili powder, cumin, garlic powder, salt, and pepper. Sear chicken for 5-7 minutes per side, until cooked through. Let cool slightly, then shred with two forks.

Make the Filling: In the same skillet, heat 1 tbsp olive oil over medium heat. Add onion and cook until softened, about 5 minutes. Add garlic and cook for 1 minute more. Stir in black beans, diced tomatoes and green chilies, and corn. Cook for 5 minutes, stirring occasionally. Remove from heat and stir in shredded chicken and cilantro.

Assemble the Enchiladas: Preheat oven to 375°F (190°C). Lightly grease a 9x13 inch baking dish. Pour a thin layer of enchilada sauce into the bottom of the dish.

Warm the Tortillas: Slightly warm the tortillas in a dry skillet or microwave (wrapped in a damp paper towel) to make them more pliable. This prevents tearing.

Fill and Roll: Dip each tortilla in the enchilada sauce, coating both sides. Place a generous amount of chicken filling in the center of each tortilla. Roll up tightly and place seam-down in the prepared baking dish.

Top and Bake: Pour remaining enchilada sauce over the enchiladas. Sprinkle with shredded cheese. Bake for 20-25 minutes, or until cheese is melted and bubbly, and the sauce is heated through.

Serve: Let cool slightly before serving. Garnish with extra cilantro, sour cream, or avocado, if desired.