Brown meat and onion; drain. Add taco seasoning and simmer 10 minutes.
In saucepan, heat soup, milk and Velveeta cheese. Heat on low until cheese melts. Add ranch dip mix, green chilies and pimentos.
Put a small amount of cheese mixture in bottom of casserole dish. Fill tortillas with meat, grated cheese and about 2 tablespoons of cheese sauce mixture. Roll up and place filled tortillas in dish. Cover with foil and bake for 30 minutes at 350º.