I brought these marinated cooked and peeled prawns from Tesco for my lunch at work. Can I heat these up in the microwave so I can enjoy them warm/hot, and if so how long will they take to heat?
My best method for reheating frozen prawns is to cover them with hot liquid. Broth is good, but water works. I even just use hot tap water. In a few minutes they are ready to eat. Even if I am adding them to a dish, I thaw them in warm water and add after I have taken the pot off the flame. Frozen shrimp just get rubbery too easily.
If they are marinated, I would heat them slowly in butter (and personally add plenty of garlic).
Defrosting prawns in a microwave is an accepted technique if power is on the lowest defrost setting, but warming prawns with a microwave makes them chewy and hard. If necessary you could warm them on defrost and just go by touch to see if they are up to temperature.
If you are concerned about longevity, microwaving prawns won't prolong their shelf life particularly, unless you absolutely nuke them, and they become chewy at least as fast as they become warm.
If they have been stored somewhere hot all day, ignore the above and destroy them.