Preheat oven to 350°F and lightly grease a 9x13 inch casserole dish with cooking spray or butter.
Cook pasta according to package directions until just al dente, about 1-2 minutes less than recommended. Drain and rinse with cool water to stop the cooking.
In a large mixing bowl, combine the cooked pasta, shredded chicken, corn, diced tomatoes, and red onion. Toss gently to distribute everything evenly.
In a separate small bowl, whisk together the ranch dressing and BBQ sauce until smooth and fully combined.
Pour the sauce mixture over the chicken and pasta mixture. Add 1 1/2 cups of the shredded cheese, salt, and pepper. Stir until everything is coated and the cheese is distributed throughout.
Transfer the mixture to your prepared casserole dish, spreading it out evenly. Top with the remaining 1 cup of cheese, making sure to cover the surface completely.
Bake uncovered for 20-25 minutes until the cheese is melted and bubbly, and the edges are just starting to turn golden.
Let it rest for 5 minutes before serving. Garnish with sliced green onions and optional bacon bits if desired.