Heat oven to 200C/fan 180C/gas 6. Put the bread into the bowl of a food processor and whizz until you have rough crumbs. Add the curry paste and whizz again until the crumbs are fairly fine and evenly coated in the curry paste.
Put the fish fillets onto a baking sheet or tray, season on both sides, then grate the zest of half the lime on top. Gently press the curry paste crumbs on top of the fish, then bake until the fish is cooked through and the topping crisp and golden, about 7 mins.
These fish fillets freeze really well raw with their topping, as long as the fish hasn’t been previously frozen. Put into the freezer on the baking tray, then when completely solid transfer to a sealed container. Cook from frozen, adding 5 more mins cooking time.