Fry the chopped onion in half the the olive oil for 2 minutes. Add the drained butter beans, stock and mint. Simmer gently.
Mix the pesto, ground almonds, lemon zest and parmesan together. Spoon onto the flesh of the salmon.
If you like crispy salmon skin, fry the salmon in the remaining oil, skin side down for 3 minutes.
Then transfer to the hot oven for 5-6 minutes to finish cooking through. If you don't eat the salmon skin you can skip frying it and just bake it for 8-9 minutes.