Preheat your oven to 375°F (190°C). Wash the bell peppers, slice the tops off, and remove the seeds and membranes. Place them upright in a baking dish.

In a medium saucepan, combine 1 cup of rinsed quinoa with 2 cups of water. Bring to a boil, then reduce heat to low, cover, and simmer for 15 minutes. Remove from heat and let sit for 5 minutes before fluffing with a fork.

In a large skillet, heat a splash of olive oil over medium heat. Add the ground turkey and cook until browned, about 5-7 minutes. Drain any excess fat.

Add the diced onion and minced garlic to the skillet with the turkey. Sauté for 2 minutes until fragrant. Stir in the cooked quinoa, black beans, corn, cumin, chili powder, salt, and pepper. Mix well.

Stuff each bell pepper with the quinoa and turkey mixture, packing it down gently. Top with shredded cheese.

Cover the baking dish with aluminum foil and bake for 25 minutes. Remove the foil and bake for an additional 10 minutes, until the cheese is bubbly and golden.

Let the stuffed peppers cool for a few minutes before serving. Garnish with fresh cilantro if desired.