Wash the fish and dab dry. Wash oranges hot, grate dry and cut 1/2 into slices. Wash coriander and lemongrass and shake dry. Cut lemongrass in half lengthwise.
Fill half of the coriander, lemongrass and orange slices into the abdominal cavities. Separate the eggs for the salt crust. Beat the egg whites with the whisks of the hand mixer until stiff. Mix sea salt, egg yolks, beaten egg whites, flour and starch.
On a baking tray lined with baking paper press one layer of salt dough (approx. 1 cm thick) next to each other in the size of the fish. Place the fish on top and gradually cover them with salt dough to an even thickness.
Press firmly again and again. Cook in the preheated oven (electric cooker: 200 °C/ convection oven: 175 °C/ gas: level 3) for 25-30 minutes. Wash potatoes thoroughly and cook in boiling water for about 20 minutes.
For the mojo, rub the peel of the remaining oranges thinly. Squeeze the juice of 1/2 orange. Wash and clean the chillies and cut into thin rings. Chop the rest of the coriander, except for a little bit for garnishing.
Peel the garlic and press it through a garlic press. Mix chili, coriander, orange peel, oil and 4 tablespoons of orange juice. Season with salt. Open the salt crust of the fish. Remove the skin from the fish, fillet the fish.
Arrange potatoes, mojo and fish and garnish with coriander.