1Cook beef and onion in 12-inch skillet over medium-high heat about 10 minutes, stirring occasionally, until beef is brown; drain. Return beef mixture to skillet; stir in taco seasoning mix and water.
2Spray 3 1/2- to 4-quart slow cooker with cooking spray. Cut chiles in half; remove seeds. Arrange half of the chiles evenly over bottom of cooker. Spoon in beef mixture. Spoon refried beans over beef in an even layer. Top with remaining chiles. Pour salsa over all.
3Cover and cook on low heat setting 8 to 10 hours or until bubbling. For each serving, place about 1 cup tortilla chips on plate, spoon ground beef mixture over chips and top with about 1/3 cup of the cheese. Ground beef mixture will hold on low heat setting up to 2 hours. Stir occasionally.