First, I preheat the oven to 350 °F (175 °C). Meanwhile, I lightly grease a 9×13-inch baking dish so the casserole won’t stick. This gives me time to get everything else ready.
In a large skillet over medium-high heat, I heat the vegetable oil and then add the cubed chicken. I sauté it until it's cooked through—about 6 to 8 minutes—stirring occasionally so the pieces brown evenly.
Once the chicken is cooked, I stir in the taco seasoning, black beans, drained corn, and salsa. I add just enough water to prevent dryness, stir well, then cover and simmer over medium-low heat for 10 minutes so all the flavors marry.
I transfer that flavorful chicken mixture into the greased baking dish, spreading it evenly. Then I sprinkle half (½ cup) of the shredded cheese over the top, followed by the crushed tortilla chips. I bake it for 15 minutes.
After 15 minutes, I add the remaining cheese (½ cup), and bake a few more minutes until it's melted, bubbly, and golden. Then I let it cool for a few minutes before serving so it sets up nicely.