Cook the rice. Prepare the rice according to the package directions. Once cooked, fluff with a fork and set aside.
Season the chicken. Place the diced chicken in a large bowl. Drizzle with olive oil and sprinkle with 2 tablespoons Cajun seasoning or your preferred all-purpose seasoning. Toss until evenly coated.
Cook the chicken. Heat 2 tablespoons olive oil in a large skillet over medium heat. Add the chicken in a single layer, working in batches if needed. Cook for approximately 3 minutes per side, flipping once, until golden and the internal temperature reaches 165°F. Transfer to a bowl and loosely tent with foil.
Sauté the garlic. Reduce the skillet heat to medium-low. Add the butter and allow it to melt, then stir in the minced garlic. Cook for 30–60 seconds until fragrant, without browning.
Season the sauce. Stir in the Cajun seasoning, black pepper, red pepper flakes and salt. Slowly whisk in the half-and-half until combined.
Thicken the sauce. Bring to a gentle simmer and cook for approximately 3–5 minutes, stirring occasionally, until slightly thickened. Reduce the heat to low and stir in the Parmesan until completely melted and smooth.
Finish the sauce. Turn off the heat and stir in the lemon juice and fresh parsley. Taste and adjust the seasonings as needed.
Assemble. Preheat the oven to 375°F. Generously butter a 9×13-inch baking dish. Spread the cooked rice in an even layer, followed by the cooked chicken. Pour the garlic Parmesan sauce evenly over the chicken and rice, making sure it reaches the edges. Sprinkle the shredded Colby Jack or pepper jack cheese evenly over the top.
Bake. Bake uncovered for 20–25 minutes, or until heated through, with the cheese fully melted and the edges golden and bubbly. For extra browning, broil for 1–3 minutes, watching carefully.
Serve. Let rest for approximately 5 minutes before serving.