Heat the oil in a medium heavy-based frying pan and cook the potatoes over a high heat for 3–4 minutes until golden in places. Add the bacon and cook for a further 5 minutes until golden, stirring occasionally. Add the peas and the measurement water and bring to the boil. Cover with a baking sheet and cook for a further 2–3 minutes.
Meanwhile, beat the eggs with the mustard and season generously with pepper.
Remove the baking sheet from the top of the pan, pour in the eggs and mix well to evenly distribute the filling and make sure any surplus water mixes with the eggs. Cook for 2–3 minutes until the base is set, then place the pan under a preheated grill (keeping the handle away from the heat) and cook for a further 2 minutes until the top is golden and set.