2 teaspoons extra-virgin olive oil 1 cup finely chopped sweet onion 1/2 cup chopped red bell pepper 1/2 cup chopped green bell pepper 1/2 cup chopped cremini mushrooms 1 teaspoon Worcestershire sauce 1/4 teaspoon minced fresh thyme 1/4 teaspoon kosher salt 1/4 teaspoon black pepper 12 ounces 90% lean ground sirloin Cooking spray 1 ounce reduced-fat provolone cheese, shredded (about 1/4 cup) 8 (1-ounce) slider buns

1. Preheat broiler.
2. Heat oil in a large skillet over medium-high heat. Add onion, bell peppers, and mushrooms; sauté 5 minutes. Combine onion mixture and next 5 ingredients (through beef) in a bowl. Shape beef mixture into 8 (1/3-inch-thick) patties.
3. Heat a grill pan over high heat; coat with cooking spray. Cook patties 3 minutes; turn, top with cheese, and cook 2 minutes.
4. Arrange buns, cut sides up, on a baking sheet; broil 30 seconds. Assemble sandwiches.