Place a large saucepan of salted water to boil over medium/high heat. Add the pasta and cook as per pack instruction. Remove from the heat, drain and cool. Keep aside until needed.
In a saucepan, over medium heat, drizzle the oil over the fish and place the fish in the pan. Season and cook for 2 minutes. Flip the fish and add the butter and mussels. Cook and baste the mussels and trout with the foaming butter for a further 2 minutes or until the mussels are fully opened. Add a squeeze of lemon juice and turn off the heat.
In the meantime, in a bowl, combine the pasta with the red onion, pepper, broad beans, fresh coriander, pesto and a drizzle of olive oil. Toss to combine and check the seasoning.
Break the fish into pieces and add the fish and mussels to the pasta bowl without the butter.
Toss once more and serve immediately with some extra coriander leaves.