Boil the potatoes til soft, roughly 20 minutes

While the potatoes boil you can boil the peas, or throw them in a bowl with a bit of water and microwave covered for 3 minutes

Microwave or heat the gravy on the stove as per directions

When the potatoes are ready, strain them well, return them to the pot and mash with the butter/margarine, milk/cream, salt and pepper

tear up the roast beef, place it on the bread slice and microwave for 30 seconds to heat the meat and soften the bread a little

Cover. Everything. In gravy.