Heat the oil in a pan, season the salmon on both sides, then fry for 4 mins each side until golden and the flesh flakes easily. Leave to rest on a plate while you cook the spinach.
Tip the leaves into the hot pan, season well, then cover and leave to wilt for 1 min, stirring once or twice. Spoon the spinach onto plates, then top with the salmon. Gently heat the crème fraîche in the pan with a squeeze of the lemon juice, the capers, corn and parsley, then season to taste. Be careful not to let it boil. Spoon the sauce over the fish, then serve with lemon wedges.