In a large skillet, heat olive oil and sauté onion and garlic until soft and translucent. Add ground beef or turkey, cooking until browned. Add taco seasoning spice packets, stirring to combine well. Add cilantro, bell pepper, diced green chiles and salsa and cook for several minutes to soften. Stir in black beans and corn, combining gently. Simmer for 15 minutes. Meanwhile, prepare the casserole dish. Line the bottom of a lightly greased or buttered 9 x 13 inch casserole dish. Cover the bottom with half of the flour tortillas. (Tip: If you cut the tortillas in half, the cut site will fit nicely into the edges of all four sides of the pan.) Warm the refried beans in the microwave for about 45 seconds for easier spreading. Lightly spread the refried beans over the tortillas. Sprinkle one cup of the cheese over the refried beans. (Use more if desired.) Spoon one half of the meat mixture over the cheese. Repeat the process for the second layer. Top with remainder of cheese, or more cheese if desired. Bake in 350 degree oven for 30 minutes. (Optional, cover with foil and bake for 20 minutes, then uncover and bake for another 10 minutes or until cheese is melted and bubbling. Cut into portion and serving for toppings and sour cream on the side.