To prepare sauce, blend tomatoes and their liquid with onion and garlic in a blender or food processor. Pour into a medium sized sauce pan. Add the red pepper, salt and tomato paste. Heat to a boil, then simmer for 5-10 minutes.
Place 3 tortillas in the bottom of the crock pot. Layer 1/3 of the ground beef, 1/3 of the tomato sauce and 1/3 of the cheese. Repeat each layer two more times.