01 - Preheat oven to 400°F. Grease a 9x13-inch baking dish with cooking spray or a small amount of oil.
02 - Heat olive oil in a large skillet over medium heat. Add diced onion and cook for 2–3 minutes until softened and translucent.
03 - Stir in minced garlic and cook for 30 seconds until fragrant, being careful not to burn it.
04 - Add ground turkey to the skillet, breaking it up with a wooden spoon. Cook for 5–6 minutes until completely browned and no longer pink.
05 - Add red bell pepper, diced sweet potatoes, dried thyme, oregano, smoked paprika, salt, and black pepper. Stir well to combine and cook for 5 minutes, stirring occasionally.
06 - Pour in chicken broth and bring to a gentle simmer. Continue cooking for 8–10 minutes until sweet potatoes are just tender when pierced with a fork.
07 - Remove skillet from heat. Fold in chopped spinach and stir until wilted from the residual heat.
08 - Transfer the turkey and vegetable mixture into the prepared baking dish, spreading it evenly. Sprinkle mozzarella and Parmesan cheese uniformly over the top.
09 - Bake for 18–20 minutes until the cheese is fully melted, golden brown, and the casserole is bubbling around the edges.
10 - Let the casserole rest for 5 minutes before serving to allow the flavors to meld and make serving easier.