Three-Cheese Florentine Burgers

1 1/3 Cups Fresh Baby Spinach
1 Tablespoon Plus 1 Teaspoon Balsamic Vinaigrette

BURGERS:
1 Egg
1/3 Cup Fresh Baby Spinach, Finely Chopped
3 Tablespoons Crumbled Feta Cheese
3 Tablespoons Shredded Asiago Cheese
3 Tablespoons Chopped Red Onion
1 Tablespoon Plus 1 Teaspoons Ketchup
2 Teaspoons Worcestershire Sauce
Teaspoon Salt
Teaspoon Pepper
1 Pound Ground Beef
4 Ounces Fresh Mozzarella Cheese, Sliced
4 Whole Wheat Hamburger Buns, Split

1. Place spinach in a small bowl.  Drizzle with vinaigrette and toss to coat; set aside.
2. In a large bowl, combine the egg, spinach, cheeses, onion, ketchup, Worcestershire sauce, salt and pepper.  Crumble beef over mixture and mix well.  Shape into four patties.
3. Grill burgers, covered, over medium heat or broil 4 inches from the heat for 5-7 minutes on each side or until a meat thermometer reads 160F and juices run clear.  Top with mozzarella cheese.  Grill 1-2 minutes longer or until cheese is melted.  Serve on buns with spinach mixture.