Preheat the oven grill to medium hot (about 180C/350F).
Lightly beat the eggs, grated cheese and the chopped parsley together in a bowl. Season with a little salt and plant of black pepper.
Pan fry the bacon in a non-stick frying pan until crisp, then drain on kitchen towels. Chop half into small cubes and add to the eggs.
Add the sliced mushrooms in the same pan as the bacon and cook for 3-4 minutes. Set aside.
Wipe the skillet with the oil and heat on the stove. Add a half of the egg mixture into the skillet and as soon as it starts to cook, layer some mushrooms, sliced cooked sausage and tomatoes over the top.
Continue to cook until the middle starts to set, adding the rest of the beaten eggs on top. Layer the remaining bacon, mushrooms, tomatoes and sausages over the top, letting them sink into the eggs.
Once the frittata is set at the edges with a wobble in the middle, sprinkle with a little finely grated Comté, transfer to the oven and cook for a further 20-30 minutes or until set.
Leave the frittata in the skillet for 10 minutes (it will remain piping hot) and then remove with a spatula onto a warmed plate. Serve immediately or leave to cool completely before eating.