Grate the lemon peel into a small bowl to get the zest. Reserve the lemon juice in another small bowl.
Put fish pieces in a large bowl. Add half the lemon juice, salt, crushed peppercorns and ginger-garlic paste. Mix and set aside to marinate for 1 hour.
Blend together almonds, pinenuts, pistachios, melon seeds and pumpkin seeds into a coarse mixture. Spread the mixture on a plate.
Add chilli flakes, semolina, parmesan cheese powder, breadcrumbs, salt and crushed peppercorns and mix.
Take the beaten egg in a bowl, dip marinated fish pieces in it and coat with nut-breadcrumb mixture.
Heat some oil in a non-stick pan. Place the fish pieces in it and shallow-fry, turning sides, till golden brown and evenly done on both sides.
To make lemon butter sauce, heat butter in a non-stick pan. Add remaining lemon juice and coriander leaves, mix well and cook for 2-3 minutes.
Serve the fish hot with lemon butter sauce.