1. Preheat oven to 350°F. Lightly coat a 2-quart rectangular baking dish with cooking spray; set aside. Cook gnocchi according to package directions. Drain. Transfer to a large bowl. Stir in pasta sauce; set aside.

2. Meanwhile, in a large bowl combine ground beef, the chopped onion, egg, bread crumbs, oregano, basil, garlic powder, and fennel seeds. Shape meat mixture into 24 balls.

3. In a large skillet heat 2 teaspoons olive oil over medium heat. Add mushrooms, sweet pepper, and the sliced onion; cook about 7 minutes or until tender. Add vegetables to bowl with gnocchi.

4. In the same large skillet heat 2 teaspoons oil over medium heat. Cook meatballs, half at a time, about 6 minutes or until cooked through (160°F), turning occasionally. Transfer meatballs to bowl with gnocchi and vegetables. Stir gently to combine.

5. Pour gnocchi mixture into prepared baking dish. Cover with foil. Bake for 20 minutes. Sprinkle cheese on top. Bake, uncovered, about 10 minutes more or until cheese is melted and golden brown.

To Make Ahead:

Prepare as directed through Step 4. Pour gnocchi mixture into prepared baking dish. Cover with foil. Chill for 4 to 24 hours. To serve, preheat oven to 350°F. Bake, covered, for 45 minutes; stir. Sprinkle cheese on top. Bake, uncovered, for 10 to 15 minutes more or until cheese is melted and golden brown.