In a large nonstick pan, add ground beef and onions. Sprinkle in taco seasoning. Brown beef and onions while breaking up beef. Drain any fat. Add meat mixture to crock-pot. Stir in salsa, sour cream, refried beans, condensed cheese soup, and fat-free milk. Mix well.
Cover crock-pot and cook on High Heat for 45 minutes to 1 hour, until heated through. Once done, stir in ½ cup cheese. Top with tomatoes and remaining ½ cup cheese. Cover for about 2 minutes to melt the cheese.
Turn crock-pot to low or warm and serve dip from crock-pot with reduced-fat tortilla chips, crackers, or even carrots and celery on the side.
Leftovers freeze great! I pack them in ½ cup, 1 or 2 cup containers. Defrost and heat when ready to serve. Perfect for a healthy snack or for last-minute company.