**Preheat the Oven:** Preheat your oven to 375°F (190°C).
**Cook the Sweet Potatoes:** In a large pot, bring water to a boil and add the diced sweet potatoes. Cook for 10-12 minutes, or until tender. Drain and set aside.
**Cook the Ground Turkey:** While the sweet potatoes cook, heat the olive oil in a large skillet over medium heat. Add the ground turkey and cook for 5-7 minutes, breaking it apart with a spoon until browned and cooked through.
**Add Vegetables:** Add the diced onion, bell pepper, and minced garlic to the skillet with the turkey. Cook for an additional 3-4 minutes, or until the vegetables have softened.
**Add Tomatoes and Seasonings:** Stir in the diced tomatoes, ground cumin, chili powder, salt, and pepper. Cook for 3-4 more minutes, allowing the flavors to combine.
**Assemble the Bake:** In a greased baking dish, layer the cooked sweet potatoes on the bottom. Top with the turkey and vegetable mixture, spreading it evenly over the sweet potatoes.
**Bake:** If using cheese, sprinkle the shredded cheddar cheese on top of the casserole. Bake for 15-20 minutes, or until the cheese is melted and the casserole is heated through.
**Serve:** Garnish with chopped cilantro and serve hot.