Heat a small amount of butter in a pan and add the whisked eggs two at a time.
Cook for 2-3 minutes to make an omelette.
Slice the bagels in half and add the omelette to one side and a cheese slice to the other.
Wrap in baking paper and air fry at 180°C for 2 minutes, or until. the cheese has melted.
Notes
Do not overcook the omelette when first preparing it. It needs to be completely set, but cooking it until dry can make it rubbery after reheating.
Shape the omelette as it cooks. Folding the edges towards the centre creates a thick, round portion that fits into the bagel more easily. You can also just fold it over to make a wedge.
Cook wet vegetables thoroughly before adding the eggs. Mushrooms, tomatoes, courgette (zucchini) and spinach can all release water, which may make the frozen bagels soggy.
Toast the cut sides of the bagel lightly before assembling if you prefer a firmer texture. This can also create a slight barrier between the bread and the filling.
Avoid overfilling the bagels. Large amounts of meat, vegetables or sauce can make them difficult to wrap and may prevent the middle from heating evenly.
Place the cheese directly next to the omelette. The warmth from the reheated egg will help it melt.
Use thinly sliced fillings so the bagel remains easy to eat. Sausage patties and bacon should fit within the edges rather than hanging out of the sides.
Make several flavours in the same meal prep session. You could make two plain egg and cheese bagels, one bacon bagel and one vegetable bagel for more variety during the week.