1. Saute sausage and onion in large skillet over medium-high heat for 5 minutes, breaking up sausage.
2. Add diced mushrooms; cook 5 minutes.
3. Remove from heat; add salt, pepper, basil, bread crumbs and cheese.
4. Press mixture onto 8 portabella caps, dividing equally. Bake on baking sheet at 375 degrees F for 20 minutes. Makes 4 servings.