In a large skillet, heat 3 tablespoons of olive oil over medium heat. Once hot, add the diced onion and red bell pepper. Sauté for about 5-7 minutes, or until the vegetables are tender and the onion is translucent.
While the vegetables are cooking, rinse 1 cup of quinoa under cold water. In a medium pot, combine the rinsed quinoa and 1 ½ cups of water. Bring it to a boil, then reduce the heat to low, cover, and simmer for about 15 minutes, or until the quinoa is fluffy and the water is absorbed. Remove from heat and set aside.
Once the vegetables are ready, add the shredded chicken, red enchilada sauce, corn, black beans, cumin, smoked paprika, black pepper, salt, and cayenne pepper (if using) to the skillet. Stir well to combine all the ingredients.
Fluff the cooked quinoa with a fork and add it to the skillet with the chicken and vegetable mixture. Stir everything together until evenly combined.
Sprinkle 2 cups of shredded Mexican cheese blend over the top of the quinoa mixture. Cover the skillet with a lid and let it sit on low heat for about 5 minutes, or until the cheese is melted and bubbling.
Remove the skillet from the heat. Serve the Cheesy Chicken Enchilada Quinoa warm, garnished with diced avocado, reserved bell pepper pieces, and minced cilantro if desired. Enjoy this hearty meal with your family or friends!