01 - Preheat oven to 400°F. Grease a 9x13-inch baking dish with cooking spray or a small amount of oil.
02 - In a large skillet, heat olive oil over medium heat. Add diced onion and cook for 2–3 minutes until softened and translucent.
03 - Add minced garlic to the skillet and cook for 30 seconds until fragrant, stirring constantly to prevent burning.
04 - Add ground turkey to the skillet, breaking it up with a wooden spoon. Cook for 5–6 minutes until browned and no longer pink.
05 - Stir in red bell pepper, diced sweet potatoes, dried thyme, oregano, smoked paprika, salt, and black pepper. Cook for 5 minutes, stirring occasionally to coat everything evenly.
06 - Pour in chicken broth and bring to a gentle simmer. Cook 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, about 1 minute.
08 - Transfer the turkey and vegetable mixture into the prepared baking dish. Spread evenly. Sprinkle mozzarella and Parmesan cheese over the top in an even layer.
09 - Bake for 18–20 minutes until the cheese is melted and golden brown, and the casserole is bubbling around the edges.
10 - Let the casserole rest for 5 minutes before serving to allow it to set and make serving easier.