Preheat the oven to 180°C, fan 160°C, gas 4. Put the salmon fillets on a baking tray, drizzle over the olive oil and bake for 15 minutes. Remove from the oven and set aside.
While the salmon is cooking, bring a large pan of water to the boil, add the pasta and cook for 10-12 minutes until al dente. Drain and put into a large serving bowl, reserving 250ml of the cooking water.
While the pasta is cooking, whizz the defrosted peas with most of the mint and 5 tablespoons cold water in a food processor. Season with freshly ground black pepper and stir into the drained pasta, adding some of the reserved pasta water if the sauce is too thick. Add the dill and courgettes and stir to combine.
Flake the salmon and gently fold it into the pasta with the lemon zest. Serve garnished with the remaining mint and some freshly ground black pepper.