Heat the olive oil in a frying pan. Season the salmon with salt and black pepper and add to the hot frying pan, skin-side down. Cook for 2-3 minutes on one side, before turning over and frying for 1-2 minutes on the other side.
To make the mushy peas, melt the butter in a saucepan. Add the peas, vinegar and a splash of hot water and cook for 3-4 minutes, or until the peas are soft.
Add the extra virgin olive oil and salt and freshly ground black pepper to taste and mash roughly.
To serve, put the mushy peas on a plate and top with the salmon, skin-side up. Garnish with lemon wedges and serve straightaway.