10 fresh basil leaves, thinly sliced
6 whole wheat hamburger buns or sourdough rolls, split
6 tbsp. crumbled feta or blue cheese
1 large onion, cut into 1/2-inch slices
6 large portobello mushrooms, stems removed
1 tbsp. olive oil
2 tbsp. balsamic vinegar
1/2 tsp. garlic powder
2 tsp. Worcestershire sauce
3 Italian turkey sausage links (4 ounces each), casings removed
1 pound lean ground beef (90% lean)