Prep: Peel and dice 2 cups sweet Vidalia or yellow onion (about 1 large). Trim, seed, and dice 1 red bell pepper; set aside a few diced pieces for garnishing. If not already done, drain and rinse 1 cup cooked black beans. Shred 3 cups chicken if needed. Mince 1/4 cup cilantro leaves and dice 1 ripe Hass avocado for garnish, if using. Measure remaining ingredients: 3 tablespoons olive oil, 1 cup quinoa (white), 1 1/2 cups water, 1 cup red enchilada sauce, 1 cup corn, 2 teaspoons cumin, 1 teaspoon smoked paprika, 1 teaspoon black pepper, 1/2 teaspoon salt (or to taste), a pinch cayenne (optional), and 2 cups shredded Mexican cheese blend.
Heat a large skillet or saucepan over medium-high heat and add 3 tablespoons olive oil.
Add the 2 cups diced onion and sauté, stirring occasionally, about 7 minutes or until the onions begin to soften.
Add the diced red bell pepper (except the reserved pieces) and sauté, stirring occasionally, 3 to 5 minutes, until the peppers begin to soften.
Add 1 cup quinoa to the pan, stir to combine with the vegetables, and let the quinoa toast for about 30 seconds while stirring.
Pour in 1 1/2 cups water, reduce the heat to low, cover the pan, and cook 10 to 15 minutes, or until all the liquid has been absorbed.
Remove the lid and fluff the quinoa with a fork.
Add 3 cups shredded chicken, 1 cup red enchilada sauce, 1 cup corn, 1 cup drained and rinsed black beans, 2 teaspoons cumin, 1 teaspoon smoked paprika, 1 teaspoon black pepper, 1/2 teaspoon salt (or to taste), and a pinch cayenne if using. Stir to combine.
Cook uncovered over medium heat, stirring intermittently, about 3 to 5 minutes, until all ingredients are warmed through. Taste and adjust salt, pepper, or spices as desired.
Reduce the heat to low, evenly sprinkle 2 cups shredded Mexican cheese blend over the top, cover the pan, and cook 2 to 4 minutes, or until the cheese has melted.
Remove from heat and garnish as desired with the diced avocado, minced cilantro, and the reserved red pepper pieces. Serve immediately.
Storage: Keep leftovers airtight in the refrigerator for up to 5 days or in the freezer for up to 3 months. Reheat gently before serving.