1Cook beef and onion in 12-inch skillet over medium-high heat about 8 minutes, stirring frequently, until beef is brown; drain.
2Spray 3 1/2- to 4-quart slow cooker with cooking spray. Mix beef mixture, taco seasoning mix, beans, tomato sauce and pepper in cooker.
3Cover and cook on low heat setting 6 to 8 hours.
4To serve, place lettuce and corn chips on individual plates. Top each with beef mixture, tomatoes, avocados, cheese and salsa. Beef mixture will hold on low heat setting up to 4 hours.