Prep Time: 10 minutes
Cook Time: 10 minutes
Combine meat, 1/2 tsp. salt and 1/4 tsp. pepper; shape into 4 patties 1/2-inch thick and about 5 inches in diameter. Grill over medium-hot coals (or broil 4 to 5 inches from heat source) 4 to 5 minutes per side or until meat is no longer pink in center.
Meanwhile, heat oil in a large nonstick skillet over medium heat. Add mushrooms and garlic; sauté 5 minutes or until liquid from mushrooms is absorbed. Stir in spinach just until wilted. Stir in remaining 1/4 tsp. salt and pepper.
Place burgers on bottoms of rolls; top with spinach mixture, cheese and roll tops.