Step 1

Preheat the oven to 350 degrees F.

Step 2

Place the turkey breast on a parchment paper-lined baking sheet and sprinkle with 1/4 teaspoon each salt and pepper. Bake until the turkey is done, about 25 minutes. Remove from the oven and let cool 5 minutes, then dice.

Step 3

Melt 4 tablespoons butter in a small saucepan over medium heat. Add the flour and cook until it bubbles and begins to smell nutty, about 2 minutes. Slowly whisk in the chicken stock and half-and-half. Bring to a boil and cook until thickened, about 5 minutes. Stir in the sour cream and season with salt and pepper. Set aside.

Step 4

Heat the oil in a large, deep skillet over medium-high heat. Add the onion, Brussels sprouts, carrots and bell pepper and sauté until the vegetables begin to become tender, about 5 minutes. Season with 1/2 teaspoon each salt and pepper.

Step 5

Combine the vegetables, rice, turkey, white Cheddar and 1 cup yellow Cheddar in a large bowl. Spoon the mixture into a lightly greased 9-by-13-inch baking dish. Melt the remaining 4 tablespoons butter in a small bowl or microwave-proof glass measure, then add the panko and stir to combine. Sprinkle over the top along with the remaining cup yellow Cheddar.

Step 6

Cover the casserole with aluminum foil and bake for 30 minutes. Uncover and bake until the liquid is absorbed, the rice is tender and the cheese is melted, about 15 more minutes.