Chicken and Rice Casserole

INGREDIENTS

• Cooking spray
• 1 cup chopped onion
• 1 (8-ounce) bone-in chicken breast half, skinned
• 1/2 teaspoon black pepper, divided
• 1 (14-ounce) can fat-free, less-sodium chicken broth
• 1 tablespoon butter
• 1 (8-ounce) zucchini, halved lengthwise and thinly sliced
• 1 (8-ounce) yellow squash, halved lengthwise and thinly sliced
• 2 cups cooked long-grain white rice
• 1 teaspoon minced fresh rosemary
• 1 1/2 tablespoons all-purpose flour
• 1 1/2 cups 2% reduced-fat milk
• 1/2 cup (2 ounces) grated fresh pecorino Romano cheese, divided
• 1/4 teaspoon salt