Put the quinoa in a small saucepan and add 400ml boiling water. Simmer for 10 minutes, or until just cooked but still with a bit of bite. Drain and set aside to cool.
Preheat the oven to 200°C/gas mark 6. Cook the butternut squash chips according to the instructions on the packet.
Meanwhile, put the cooled quinoa, oats and pumpkin seeds in a mini food processor and blitz, keeping the texture quite chunky. In three large shallow bowls, line up the flour, egg and quinoa crumbs. Dip each sea bass fillet, first in the flour, then in the egg and finally in the quinoa, pressing the crumb so it sticks to the fillet on both sides.
Heat the oil in a large frying pan and fry the fish for 3-4 minutes on each side, or until the fish is golden and crunchy. Place on a baking tray and cook for a further 5 minutes in the oven to ensure the fish is cooked through.
Meanwhile, cook the peas. Drain and roughly mash with a potato masher. Stir through the crème fraîche, mint and lemon juice and season with black pepper. Serve the fish with the squash chips and minted peas on the side.