For the vinaigrette, whisk vinegar, salt, pepper and sugar. Add the oil drop by drop. Peel the shallot, cut into fine cubes and stir into the vinaigrette. Wash, clean and slice the tomatoes
Wash the chervil, shake dry, pluck the leaves from the stems. Cut the avocado in half, remove the core, remove the flesh from the skin. Peel garlic. Puree cream cheese, garlic, avocado, lemon juice and chervil, except for a little bit for garnishing, with a hand blender. Season to taste with salt and pepper
Arrange tomato slices on plates. Drizzle with vinaigrette. Break the trout filet into small pieces. Shape avocado mousse with 2 tbsp. into dumplings. Arrange mousse dumplings and trout pieces on the tomato slices. Garnish with chervil