Leftover lasagna can be reheated in the microwave or oven. Reheating lasagna in the oven makes more sense if there are a few servings left and if you are not in a rush. Microwaving leftovers is quicker, but it can be messy. To reduce the mess when microwaving it, put the lasagna to be reheated in a bowl and place a paper towel over the bowl. I suggest microwaving in 30 second increments, until it is heated through. Refrigerated lasagna can be reheated in an oven at 350 degrees for about 30 minutes.