Combine the ginger and garlic paste, black pepper, garam masala, coriander, cumin, chilli powder, vegetable oil, salt, lemon juice, and yoghurt in a bowl.
Rub the marinade into the grey mullet and let it sit for 30 minutes.
Preheat the grill to high and cook the fish for 2-3 minutes per side.
Baste the fish with lemon juice, melted butter, and chat masala during cooking.
Heat olive oil in a frying pan and fry the ceps, garlic, lemon thyme, and ajwain for 2-3 minutes.
Mix the remaining olive oil, curry leaves, crushed black pepper, and sugar to make a dressing.
Toss the cooked mushrooms in the dressing and serve alongside the fish.