Preheat the oven to 400°F (200°C).
In a large skillet, heat olive oil over medium heat. Add the diced onion and sauté until softened, about 3-4 minutes.
Add the ground beef or turkey to the skillet. Cook until browned and cooked through, breaking it into crumbles with a wooden spoon.
Stir in the chili powder, cumin, garlic powder, salt, and black pepper. Add the diced tomatoes, black beans, and corn. Mix well and cook for another 5 minutes until heated through. Remove from heat.
In a mixing bowl, whisk together the cornmeal, water, and milk until smooth.
Pour half of the cornmeal mixture into the pie dish and spread it evenly across the bottom.
Layer the meat and bean mixture over the cornmeal base, then pour the remaining cornmeal mixture on top.
Sprinkle the shredded cheese over the top layer.
Bake in the preheated oven for 25-30 minutes, or until the top is golden brown and set.
Remove from the oven and let it sit for a few minutes before slicing. Garnish with fresh cilantro if desired.