Put a large pan and a small pan of salted water to the boil.
Heat the oil in a large frying pan over a medium to high heat. Dab the salmon fillets dry and season with salt and pepper. Cook skin side down for about 6 minutes without moving them, until crisp and golden. Then carefully flip them over and cook them for 3 or so minutes or until they are just cooked in the middle but still nice and moist and tender.
Once the water is boiling, put the peas on to cook in the small pan for 3-4 minutes until tender. Cook the pasta in the large pan for as long as directed on the pack.
Once cooked, drain the peas well and tip into a food processor, or back into the pan if using a stick blender. Add the mascarpone, parmesan, lemon juice, almost all of the mint (if using) and salt and pepper and blitz to a rough puree.
Once tender, drain the pasta and return to the pan. Stir in the pea pesto to evenly coat and divide between serving plates. Sit a piece of salmon on top of each (or children may prefer the skin removed and flesh flaked over) and serve at once with a scattering of the remaining mint (if using) and a piece of lemon for squeezing.