01 - Preheat oven to 400°F. Lightly grease a 9x13-inch baking dish and set aside.
02 - Heat olive oil in a large skillet over medium heat. Add diced onion, minced garlic, and diced red bell pepper. Cook for 3 to 4 minutes, stirring occasionally, until vegetables are softened and fragrant.
03 - Add ground turkey to the skillet along with cumin, paprika, chili powder, dried oregano, salt, and black pepper. Cook for 5 to 6 minutes, breaking up the meat with a spoon, until fully browned and no longer pink.
04 - Stir in the drained black beans and drained diced tomatoes. Simmer the mixture for 3 minutes to allow the flavors to meld. Remove from heat.
05 - Spread half of the diced sweet potatoes in an even layer across the bottom of the prepared baking dish. Spoon half of the turkey and black bean mixture over the sweet potatoes, spreading it evenly.
06 - Repeat with the remaining sweet potatoes and the remaining turkey and black bean mixture, creating a second even layer on top.
07 - Cover the baking dish tightly with aluminum foil and bake for 25 to 30 minutes, or until the sweet potatoes are nearly fork-tender.
08 - Remove the foil and sprinkle the shredded Monterey Jack or cheddar cheese evenly over the top. Bake uncovered for an additional 10 minutes until the cheese is fully melted and bubbly.
09 - Remove from the oven and let the casserole rest for 5 to 10 minutes before serving. Garnish with fresh cilantro and serve with sour cream if desired.