Preheat the oven to 375°F. Spray an 8x8 baking dish with nonstick cooking spray.
Add the diced onion to a skillet coated with nonstick cooking spray. Cook over medium heat for 3–4 minutes, until softened. Add the garlic and cook for another 30 seconds.
In a large bowl, whisk together the sour cream, light mayonnaise, lime juice, chili powder, cumin, smoked paprika, salt, and black pepper.
Stir the cooked rice, shredded chicken, corn, cooked onion and garlic, and shredded cheese into the sauce. Mix until everything is evenly coated.
Spread the mixture evenly into the prepared baking dish.
Bake uncovered for 25–30 minutes, or until the casserole is heated through and the cheese is melted.
Let the casserole rest for about 5 minutes. Sprinkle with cilantro and serve with fresh lime wedges if desired.