Heat oil in a 9-inch non-stick frying pan over medium heat. Add the potato and cook, stirring occasionally, for 8 - 10 minutes until they start to soften. Add the chicken sausage and brown for 3 - 4 minutes. Season with salt and pepper.
Pour the eggs into the pan. As the eggs set around the edge of the pan, using a spatula, gently lift the egg to allow uncooked egg to flow underneath. When eggs are almost set on the surface but still look moist, add the cheese. Slip the spatula under the omelet and fold over.
In the meantime, toast the bread.
Portion the eggs onto the bread, cut in half and serve with sliced plums.