Preheat oven to 375°F (190°C). Spray a 9x13 baking dish with cooking spray.
Cook the turkey:
In a large skillet, cook ground turkey over medium heat until browned. Drain excess liquid if needed.
Add vegetables:
Add onion, bell pepper, and zucchini. Cook until softened (5–7 minutes).
Mix in beans and corn:
Stir in black beans, corn, diced tomatoes (with juices), taco seasoning, and water. Simmer for 5 minutes.
Assemble the casserole:
Pour the mixture into the prepared baking dish. Sprinkle cheese evenly on top.
Bake:
Bake uncovered for 15–20 minutes, or until cheese is melted and bubbly.
Serve:
Let it rest 5 minutes before serving. Garnish with chopped cilantro, salsa, or fat-free Greek yogurt (optional).