For the bear garlic purée, heat the lemon zest, lime zest, ginger, lemongrass and oil in a saucepan over a low heat to a temperature of around 60C. Keep the mixture at that temperature and leave to infuse for 1 hour. Remove from the heat and leave to cool to room temperature. Filter the mixture through a fine strainer and place in the fridge for 48 hours to infuse. Blanch half of the garlic leaves in boiling, salted water for 10–15 seconds. Drain and blitz with the remaining garlic leaves in a blender. Add the infused oil and season with salt. Blend again to a purée. Adjust the seasoning, leave to cool and set aside.
For the fish, season the fillets with salt. Heat the oil in a nonstick frying pan and cook the fillets skin-side down for 4–5 minutes, or until cooked through. Transfer the fillets to a warmed plate, keeping the pan over the heat.
For the Grénobloise sauce, segment 1 lemon. Add the butter to the pan and heat until it turns a nut-brown colour. Add the lemon segments, capers, fines herbes and croûtons. Squeeze over the juice of the remaining lemon half, season with salt and set aside.
For the croûtons, cut the bread slices into 5-mm/¼-in cubes. Heat the butter in a frying pan over a medium heat, add the thyme, garlic and bread cubes and sauté until they turn golden. Transfer the cubes to kitchen towels and set aside.
For the sea herbs salad, mix all of the ingredients together in a small bowl and set aside.
To serve, gently reheat the garlic purée. Divide the purée between two warmed plates and lay the fillets on top. Spoon over the Grénobloise sauce and sprinkle with the sea herbs salad. Garnish with croûtons and serve immediately.