For the dressing, stir together the lime and orange juice, mustard, agave syrup, salt and pepper, and fold in the olive oil.
Clean, wash and halve the fennel and remove the stalk. Then cut or slice into fine strips. Peel the grapefruit so thick that the white skin is also removed. Cut out the fillets between the separating skins, catch the juice and add to the dressing. Halve the avocado, remove the stone, peel, cut into narrow wedges, drizzle immediately with a little dressing. Mix the rest of the dressing with the fennel and grapefruit, carefully fold in the avocado, season to taste.