Mix a dressing in a bowl of lemon juice, olive oil, salt and pepper.
Halve the avocados and remove the stone. Peel, dice and add to the dressing. Fillet the grapefruit and cut into pieces. Add the leaked juice and grapefruit to the avocados in the dressing. Let it steep for about 10 minutes.
Fry the salmon in a pan (this will be especially nice if you`ve got salmon with the skin on).
Arrange the salmon on plates and pour the grapefruit and avocado with the dressing on top.