Preheat oven to 350°F (175°C). Lightly spray a 9x13 baking dish with cooking spray.
Cook the turkey:
Heat a large skillet over medium heat. Add ground turkey and diced onion. Cook until the turkey is browned and the onion is soft, breaking up the turkey as it cooks.
Add seasoning and veggies:
Stir in the taco seasoning, diced tomatoes (with juices), black beans, and corn. Cook for 3–4 minutes until heated through. Remove from heat.
Prepare the biscuits:
Open the biscuit can and cut each biscuit into quarters.
Assemble the casserole:
Spread half of the meat mixture into the prepared baking dish. Layer the biscuit pieces evenly over the top. Add the remaining meat mixture over the biscuits.
Top with cheese:
Sprinkle the shredded cheese evenly over the casserole.
Bake:
Bake uncovered for 30–35 minutes, or until the biscuits are cooked through and the cheese is bubbly and slightly golden.
Serve:
Let the casserole rest for 5 minutes before slicing. Garnish with optional toppings like fat-free Greek yogurt, chopped cilantro, or salsa.