Heat 1 teaspoon olive oil in a large skillet over medium-high heat.
Add the diced 1/2 large yellow onion and 1 diced bell pepper and cook, stirring often, until softened and translucent, about 3–5 minutes.
Stir in the drained 15-ounce can of black beans, 1 cup frozen corn, 2 cups cooked brown rice, and 8 ounces cooked chicken; cook for about 2 minutes to heat through.
Pour in the 10-ounce can of enchilada sauce and stir until everything is evenly coated and heated through, about 2–3 minutes or until bubbly.
Sprinkle 1 cup shredded cheddar cheese over the skillet, cover, and cook until the cheese is melted, about 1–2 minutes.
Garnish with cilantro and serve hot.