Preheat the oven to 375°F (190°C) and grease a 9x13-inch baking dish with cooking spray or oil.
Trim any fat from the chicken. Place each piece between plastic wrap or parchment and pound to an even thickness of about 1/2 inch.
Sprinkle half of the taco seasoning evenly over both sides of the chicken and rub it in.
Heat the olive oil in a large skillet over medium-high heat. Sear the chicken 2–3 minutes per side, until lightly golden; it does not need to be fully cooked.
Transfer the seared chicken to the prepared baking dish in a single layer.
In a large bowl, combine the drained black beans, fire-roasted diced tomatoes, drained Mexicorn, diced green chilies, minced garlic, and the remaining taco seasoning; stir to mix evenly.
Spread the bean and tomato mixture over the chicken, then top with the shredded Colby or Mexican blend cheese.
Bake uncovered for 35–40 minutes, until the chicken is cooked through and reaches an internal temperature of 165°F (74°C) and the cheese is melted and bubbly.
Remove from the oven, squeeze the lime over the chicken, and serve with cilantro, sour cream, hot sauce, or diced avocado if desired.