Preheat oven (electric cooker: 200 °C/circulating air: 175 °C/gas: see manufacturer). Wash the lemon hot, dab dry and finely grate the peel. Coarsely chop the pistachios and mix with 1-2 tbsp. oil and lemon peel.
Season with salt and pepper.
Line a baking tray with baking paper. Wash the fish, dab dry. Coat with 2 tablespoons of oil and place on a baking tray. Spread the pistachios on top and press them down a little. Bake in a hot oven for 15-20 minutes, depending on the thickness of the fillets.
For the vinaigrette, mix vinegar, salt, pepper and 1 pinch of sugar. Fold in 3 tablespoons of oil. Peel the shallot, dice finely and stir into the vinaigrette with the mustard.
Clean, wash and cut the rhubarb into very thin slices. Wash and halve the tomatoes. Sort the rocket and baby salad, wash, shake dry and cut into smaller pieces if necessary. Mix vinaigrette with rhubarb, tomatoes and lettuce.
Serve with the halibut.