In a large skillet, cook beef and onion over medium heat in cooking oil until meat is no longer pink.
Add garlic; cook 1 minute longer. Drain.
Stir in the salsa, beans, tomatoes, chilis, taco seasoning, mixed veggies and pepper; heat through.
Spread 1/2 cup enchilada sauce over bottom of a greased 13x9-in. baking dish. Top with two tortillas--tear or overlap as necessary for a single layer. Top tortilla layer with 1/2 cup enchilada sauce, 1/3 cup cheese, 1/3 of the meat mixture.
Top with 2 tortillas as before. Spread 1/2 cup enchilada sauce over tortillas. Spread refried beans over enchilada sauce. Spread 1/3 of meat mixture, then layer with 1/3 cup cheese.
Top with 2 tortillas as before. Cover with 1/2 cup enchilada sauce, layer with 1/3 cup cheese, mixed veggies, remaining meat mixture and 1/3 cup of cheese.
Top with remaining tortillas. Spread remaining enchilada sauce over tortillas, top with remaining tomatoes, then remaining cheese. Scatter olives across cheese.
Cover dish with oven-safe lid or aluminum foil; bake at 375° for 30 minutes. Uncover and bake 10 minutes or until cheese starts to bubble. Remove from oven and sprinkle with chopped green onion, cilantro, parsley or other toppings. Let stand 10 minutes to cool and firm up.
Cut lasagna into serving sizes and serve. Top each serving with sour cream, guacamole, hot sauce, etc.