01 - Preheat the oven to 400°F. Lightly 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 red bell pepper, sautéing for 3-4 minutes until softened and translucent.
03 - Stir in minced garlic and cook for 1 minute 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 browned and cooked through, breaking apart any large clumps.
05 - Add smoked paprika, dried thyme, ground cumin, chili powder, salt, black pepper, and crushed red pepper flakes. Stir thoroughly to coat the turkey evenly with spices.
06 - Add chopped baby spinach to the skillet and cook for 1-2 minutes, stirring occasionally, until wilted. Remove the skillet from heat.
07 - In a large bowl, toss sweet potato cubes with a pinch of salt and pepper. Spread them evenly across the bottom of the prepared baking dish.
08 - Spoon the seasoned turkey and vegetable mixture evenly over the sweet potatoes in the baking dish.
09 - Drizzle milk evenly over the casserole. Sprinkle shredded cheddar cheese across the entire surface in a uniform layer.
10 - Cover the baking dish tightly with aluminum foil. Bake for 25 minutes to begin cooking the sweet potatoes.
11 - Remove the foil and continue baking for another 15 minutes until sweet potatoes are tender when pierced with a fork and the cheese is golden and bubbly.
12 - Let the casserole rest for 5 minutes before serving. Garnish with chopped fresh parsley if desired. Serve warm.