Preheat the oven to 375°F (190°C). Prepare a medium-sized casserole dish by lightly greasing it with a tiny amount of olive oil or lining it with parchment paper.

Sauté the Vegetables: In a large skillet, heat 1 teaspoon of olive oil over medium heat. Add the julienned red onion and cook for 2-3 minutes until it softens slightly. Next, add the garlic, diced sweet potatoes, and carrots, cooking for an additional 5-7 minutes. Stir occasionally to ensure even cooking. The vegetables should start to become tender but not fully cooked, as they’ll finish in the oven.

Prepare the Cream Sauce: In a small bowl, whisk together the cream of mushroom soup mix and 1 1/2 cups of milk until fully combined. Set this aside; it will serve as the base for the casserole's creamy texture.

Assemble the Casserole: In your greased casserole dish, start by spreading an even layer of the cooked brown rice. This will serve as the base. Then, add the cubed roasted chicken breast evenly on top of the rice. Distribute the sautéed vegetables, including the softened onions, sweet potatoes, and carrots, over the chicken. Sprinkle the dried cranberries throughout the mixture for a sweet pop of flavor. Place the halved Brussels sprouts around the casserole.

Pour the Cream Sauce: Gently pour the cream of mushroom and milk mixture over the assembled ingredients, ensuring it covers most of the dish. You can use a spoon to spread it evenly. If you're using almonds, sprinkle it over the top.

Bake: Place the casserole in the preheated oven and bake uncovered for 25-30 minutes, or until the vegetables are fully tender. If the top is browning too quickly, you can cover it loosely with foil for the remaining baking time.

Serve and Enjoy: Once the casserole is done, remove it from the oven and let it cool for 5-10 minutes before serving.