Yes, breakfast casserole can be reheated in the oven or microwave for a delicious meal. It is best to store any leftovers in an airtight container and consume them within two days of cooking. If you're planning to reheat it in the oven, preheat the oven first and then place the casserole dish on the center rack. Make sure to cover it with a lid or foil so that it doesn't dry out while baking. The baking time will depend on how much food is inside; usually, 10 minutes at 375°F should do it. If using a microwave, make sure that your container isn't too large; heat it in 30-second intervals until everything is hot enough.