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, cooking 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 apart with a wooden spoon. Cook for 5-6 minutes until completely browned and no pink remains.
05 - Sprinkle smoked paprika, dried thyme, ground cumin, chili powder, salt, black pepper, and red pepper flakes over the turkey. Stir thoroughly to combine.
06 - Add chopped spinach to the skillet and cook for 1-2 minutes, stirring until just wilted. Remove from heat.
07 - Place sweet potato cubes in a large bowl and season with a pinch of salt and pepper. Toss to coat evenly, then spread in the prepared baking dish.
08 - Spoon the turkey and vegetable mixture evenly over the sweet potato layer in the baking dish.
09 - Drizzle milk over the entire casserole, then sprinkle shredded cheddar cheese evenly across the top.
10 - Cover the baking dish tightly with aluminum foil. Bake for 25 minutes to steam the sweet potatoes.
11 - Remove the foil and return to the oven for an additional 15 minutes until sweet potatoes are tender when pierced with a fork and cheese is golden and bubbly.
12 - Let the casserole rest for 5 minutes before serving to allow the layers to set. Garnish with fresh chopped parsley if desired.