Fill a frying pan with water so that it is 5cm deep. Place on the hob and slowly bring to the boil.
Meanwhile, place the muffins under a hot grill and lightly toast. Top with the sliced tomatoes and cheese, then pop back under the grill and cook for 2 mins or until the cheese has melted. Divide between two plates and keep warm.
Carefully crack the eggs and drop them into the simmering water. Reduce the heat to a gentle simmer and set the timer for 3-4 mins, depending how runny you like your egg yolk. Remove the pan from the heat. Then use a slotted spoon to carefully remove the eggs from the water; let any water drain off the eggs, then place an egg on top of each half of muffin. Serve immediately.