Clean and wash the radicchio and cut into thin slices. Wash and drain the Batavia and pluck into bite-sized pieces. Wash, clean and halve the tomatoes. Arrange prepared ingredients on portion plates.
For the vinaigrette, peel and finely chop the onion. Wash the chives and cut into small rolls. Wash lemon, grate peel finely, squeeze juice. Mix the prepared ingredients for the vinaigrette with 3 tablespoons of water.
Season with salt, pepper and sugar, beat the oil into it. Pour over the salad. Serve garnished with lemon.