Peel the garlic and cut into fine slices. Wash parsley, dab dry and cut into strips. Pour the beans onto a sieve, rinse briefly, drain. Season lemon juice and zest with salt, pepper, sugar and garlic.
Beat olive oil into it. Add parsley. Pour the marinade over the beans. Cover and let stand for about 30 minutes. In the meantime, clean the radicchio, pluck off the leaves and wash. Line a starter plate with the radicchio.
Flavour the beans again. Arrange on the salad. Serve garnished with lemon slices.