1. Heat gas or charcoal grill. In large bowl, mix turkey, ranch dressing and taco seasoning mix. Shape mixture into 4 patties, about 4 inches wide and 3/4 inch thick.
2. Place patties on grill over medium heat. Cover grill; cook 13 to 15 minutes, carefully turning once, until meat thermometer inserted in center of patties reads at least 165°F. Top each burger with 1 slice cheese and place buns, cut sides down, on grill; cover grill and cook 1 to 2 minutes or until cheese is melted and buns are lightly toasted.
3. Place burgers on bun bottoms. Cover with bun tops.
Broiling Directions: Set oven control to broil. Place buns, cut side up, in broiler pan. Broil with tops about 6 inches from heat 2 to 3 minutes or until lightly toasted; remove from broiler pan, and set aside. Spray broiler pan with cooking spray. Place patties on rack in broiler pan. Broil 12 to 16 minutes, carefully turning once, until meat thermometer inserted in center of patties reads at least 165°F. Top each burger with slice of cheese; broil about 30 seconds or until melted.