Best way to reheat frozen cooked meatloaf?

Other than frozen entree option on microwave, you can also try steaming in a skillet: place the meatloaf in a large pan with a lid, add about 1/4-1/2 c water, cover, and steam (low to medium heat) until heated through.

First method.... I would TRY to remember to move the needed portions from the freezer to the fridge the day before I wanted them for dinner (not something that I would remember to do!). Second method... cover and microwave on 40% power for a couple minutes and check, slowly adding additional time if needed. You are only reheating, not cooking. Third method... if you are planning to add gravy or a sauce, you could put in a fry pan with the sauce, cover, and slowly heat on med-low until hot. I'd probably flip at least once to allow a more even reheating. There are only 2 of us in our house now, and we depend upon frozen leftovers to make dinners we otherwise couldn't enjoy.