1) Cut papayas lengthwise and scoop out the seeds with a spoon.
2) Remove pulp from centers of papaya halves, leaving 1/2 -inch-thick shell.
3) Peel papayas.
4) Brush insides of shells with lemon juice.
5) Chop enough pulp to measure 1/2 cup; set aside.
6) Place vanilla yogurt in a medium bowl.
7) Mix enough milk into the yogurt to make dressing of desired consistency.
8) Gently add in chopped papaya, the raspberries, and crabmeat and mix well.
9) Arrange shredded lettuce on 4 dinner plates.
10) Pour a spoonful of crab mixture into papaya shells.
11) Place papaya shells on plates and serve.