Heat olive oil in a large skillet or Dutch oven over medium heat. Add the onion and pepper, and cook until softened and translucent, about 5 minutes.
Increase heat to medium-high and add the cooked chicken. Stir to heat through and break up any large pieces.
Add the cooked rice and stir to combine with the chicken and vegetables. Cook for 1-2 minutes, allowing the rice to warm through.
Drizzle the enchilada sauce on top.
Sprinkle the shredded cheddar cheese evenly over the mixture.
Reduce heat to low, cover the pan, and simmer for 5-7 minutes, or until the cheese is melted and bubbly.
Remove from heat and let stand for a few minutes before serving.
Top with your favorite toppings! Chopped lettuce, salsa, diced avocado, sour cream, chopped cilantro, and jalapenos are all great options.