Preheat the oven. Set to 375°F (190°C).
Lightly grease a 9x13-inch baking dish.
Cook the chicken. Season with 1 tablespoon taco seasoning, salt, and pepper. Sauté in a skillet with 1 tablespoon olive oil over medium heat until cooked through, 6–8 minutes per side for breasts (or 5–6 minutes for bite-size pieces). Let rest, then shred or dice.
Shortcut: use rotisserie chicken.
Sauté the veggies. In the same pan, add a splash of oil if needed. Cook diced bell peppers and red onion with a pinch of salt until softened, about 5–7 minutes. Stir in remaining taco seasoning for 30 seconds to bloom the spices.
Mix the base. In a large bowl, combine cooked rice, black beans, corn, sautéed veggies, salsa, tomato sauce, half the cheese, and the cooked chicken.
Add lime zest and a squeeze of lime juice. Taste and adjust salt or seasoning as needed.
Assemble. Spread the mixture evenly in the prepared baking dish. Top with the remaining cheese.
Add jalapeño slices if you like heat.
Bake. Cover with foil and bake for 15 minutes. Remove foil and bake another 10–15 minutes, until hot and bubbly and the cheese is lightly golden.
Finish and rest. Let the casserole sit for 5 minutes. Sprinkle with chopped cilantro and another squeeze of lime for brightness.
Serve. Spoon into bowls and add your favorite toppings: sour cream, avocado, green onions, extra salsa, or hot sauce.