Green Salad - A simple green salad with a light vinaigrette can add a nice, crisp contrast to the richness of most casseroles. Toss in some cherry tomatoes, cucumbers, and maybe a sprinkle of nuts for crunch.
Steamed Veggies - Broccoli, green beans, or asparagus, steamed and seasoned with a bit of salt, pepper, and lemon juice, can add a bright and healthy side to your meal.