Prepare the grapefruit : peel it and remove the white parts. Cut the pulp into small slices and set aside. Keep the grapefruit juice for later.
Shell the shrimps and cut them into small slices. In a bowl, combine shrimps, grapefruit, olive oil, 1/2 lemon juice, paprika and salt. Refrigerate.
Cut the avocado, remove the stone and blend the flesh with 1/2 lemon juice and salt.
Put some spoons of avocado in the glasses and the grapefruit + shrimps preparation on top. Refrigerate before eating. There you are, your verrines are ready !