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 - 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 fully 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 combine flavors.
06 - Pour in chicken broth and bring to a gentle simmer. Cook for 8–10 minutes until sweet potatoes are fork-tender but not mushy.
07 - Remove skillet from heat. Fold in chopped spinach and stir until just wilted from the residual heat.
08 - Transfer the turkey and vegetable mixture into the prepared baking dish, spreading it evenly. Sprinkle mozzarella and Parmesan cheeses over the top in an even layer.
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.