Uncle Al's Sausage and Peppers Casserole

INGREDIENTS

• 2 tablespoons chopped basil leaves, plus some for garnish
• 1 red bell pepper, cored, seeded, and cut into 1- inch-wide strips
• Shaved Parmesan, for garnish
• 1 pound green beans, ends trimmed and halved
• 1 medium red onion, quartered and separated
• 1 green bell pepper, cored, seeded, and cut into 1-inch-wide strips
• 4 marinated hot cherry peppers, optional
• Equipment: oval gratin dish
• 1/4 teaspoon crushed red pepper flakes
• 3 cloves garlic, chopped
• 1/4 teaspoon freshly ground black pepper
• 1 (14-ounce) can no-sugar-added diced tomatoes
• 8 ounces button mushrooms
• 1 teaspoon dried oregano
• 1 yellow bell pepper, cored, seeded, and cut into 1- inch-wide strips
• 2 pounds fresh turkey sausage (about 8 links), cut in 1/2
• 1/4 cup olive oil