Preheat your oven to 425º F.
Heat olive oil in a large cast iron skillet over medium-high heat.
Pat the chicken dry with paper towels and rub them well with the taco seasoning on both sides, then add them to the pan. Sear the chicken on both sides. The chicken breasts will only need about 3-5 minutes per side, depending on how thick they are. You don't want to cook them through. You just want to get some flavor going on the exterior of the chicken and in the pan.
When the chicken is seared, remove it from the pan and transfer to a paper towel-lined plate; set aside.
Add the chopped onions and bell peppers to the hot skillet. Simmer them until they've softened—about 5 minutes. Then, stir in the rice and let it toast for about a minute. Finally, add the black beans, corn, chicken stock, and salsa to the pan. Stir everything together.
Nestle the chicken breasts into the rice mixture. Spoon some of the salsa over top of the chicken breasts to lightly coat, and then top them with the shredded cheese. (See recipe notes.)
Transfer the pan to the oven, uncovered, for about 20-25 minutes or until the rice is tender and the chicken is cooked through to an internal temperature of 165º F. Once the chicken and rice are done, remove the pan from the oven and top with some freshly chopped parsley or cilantro. You can also serve with jalapeños, avocado or guacamole, sour cream, or plain Greek yogurt.