Preheat the oven to 375°F (190°C).
In a large skillet, heat the olive oil over medium heat. Add the diced onion and cook until softened, about 3-4 minutes.
Add the minced garlic, ground turkey, cumin, chili powder, salt, and black pepper. Cook until the turkey is browned and cooked through, about 6-8 minutes.
Stir in the black beans and corn, mixing well. Remove from heat.
Spread 1/2 cup of the enchilada sauce on the bottom of a 9x13-inch baking dish.
To assemble the enchiladas, place about 1/4 cup of the turkey mixture in the center of each tortilla. Sprinkle with a little cheese, then roll up tightly and place seam-side down in the baking dish.
Once all tortillas are filled and placed in the dish, pour the remaining enchilada sauce over the top and sprinkle with the remaining cheese.
Cover the dish with aluminum foil and bake for 20 minutes. Remove the foil and bake for an additional 10 minutes, or until the cheese is bubbly and golden.
Let cool for a few minutes before serving. Garnish with fresh cilantro and serve with sour cream if desired.