Beef Burgers with Mushroom and Onion Topping

8 oz. white mushrooms
1 tsp. oil
1 large red onion (12 oz.), halved and thinly sliced
1/8 tsp. salt
1 tbs. balsamic vinegar
1 1/2 tbs. chopped parsley
1 tbs. Worcestershire sauce
1/8 tsp. pepper
3/4 lb. extra-lean ground beef
4 Kaiser rolls (optional)

Finely chop enough mushrooms to make 1/2 cup; slice the rest and set aside. Coat a medium nonstick skillet with cooking spray and warm over medium heat. Add chopped mushrooms and cook, stirring frequently, 4-5 minutes, until lightly browned. Place in a medium bowl and set aside to cool. Heat oil in same skillet over medium heat. Add onion, sliced mushrooms, and salt. Cover and cook, stirring occasionally, 10-12 minutes, until very soft and lightly browned. Uncover, increase heat to high, and stir in vinegar; toss to coat vegetables completely. Meanwhile, make burgers. Add parsley, Worcestershire sauce, and pepper to chopped mushrooms. Add beef and mix lightly to combine. Shape into 4 1/2"-thick patties. Heat broiler; coat broiler rack with cooking spray. Broil burgers 6" from heat source 5-6 minutes per side, or until cooked through. Serve on rolls. If desired, topped with onions and mushrooms.

Serves 4.

from the kitchen of Brenda