Preheat oven to 350°F and lightly grease a 9x13-inch baking dish.
Heat oil in a skillet over medium-high heat. Season chicken with salt and pepper, then cook for 3–4 minutes per side until fully cooked. Let rest, then cut into bite-sized pieces.
Cook the rotini pasta according to package directions. Drain and rinse with cold water.
In a large bowl, combine the cooked pasta, chicken, corn, tomatoes, red onion, and 1½ cups of shredded cheese.
Add the ranch dressing and barbecue sauce. Stir until everything is evenly coated. Season with additional salt and pepper if needed.
Transfer the mixture to the prepared baking dish and spread evenly. Top with the remaining ½ cup of cheese.
Bake for 15–20 minutes, until the cheese is melted and bubbly.
