Remove seeds and core from the red and green bell peppers, then slice them into thin strips about 1/4 inch wide. Chop the yellow onion finely, roughly one cup in volume. Cut the chicken into bite-sized pieces around 1 inch and sprinkle with kosher salt.
Warm the vegetable oil in a large skillet over medium-high heat until hot and shimmering. Add the chicken pieces, chopped onions, sliced bell peppers, and the taco seasoning packet. Stir frequently and cook for approximately 5 to 8 minutes until the vegetables have softened.
While the chicken and veggies cook, drain and rinse the black beans.
Add the black beans, diced tomatoes with their juice, instant brown rice, and chicken broth to the skillet. Mix everything well and bring the mixture to a rolling boil.
Lower the heat to a simmer, cover the skillet, and let it cook for 8 to 10 minutes until the rice is tender and the chicken is fully cooked.
Turn off the heat and keep the skillet covered. Let the dish sit for 5 minutes to allow the rice to absorb any remaining liquid.
Sprinkle the shredded Mexican cheese over the dish and top with your choice of chopped cilantro, diced avocado, sour cream, or pickled jalapeños before serving.
