Preheat the oven to 350 F. Lightly spray a 7x11 baking dish and set aside.
In a large cast-iron skillet, heat oil over medium heat. Add onions and garlic and sauté for 5 minutes, stirring frequently. Once onions are translucent and fragrant, add bell peppers and sauté 5 more minutes until peppers are cooked all the way through.
Stir in chili powder, cumin, and salt, coating the pepper/onion mixture completely.
Add black beans, corn, and kale. Cook until any liquid is absorbed and the kale has begun to wilt slightly. Remove from heat and add ½ cup enchilada sauce, stirring to combine.
Spread evenly another ½ cup of enchilada sauce on the bottom of the prepared 11x7 baking dish. Pour the remaining enchilada sauce into a shallow dish. Dip one tortilla into the enchilada sauce. Set the sauce-soaked tortilla on a plate. Add about ½ cup of filling inside the tortilla and roll up. Place the tortilla seam side down in the baking dish. Repeat with the rest of the tortillas, fitting them snuggly next to each other until all 6 tortillas and the filling are used up. Pour the remaining enchilada sauce over the top.
Bake, uncovered, for 30 minutes until sauce begins to boil at the edges.
Remove from oven and let cool 15 minutes before topping with avocado, green onions, and cilantro. Serve immediately.