Combine the shrimp, mushrooms, and grapes in a large mixing bowl. [I know, right now you're hoping I'll just stop there. I'm not sure I can think of three ingredients less likely to mingle pleasingly in a large mixing bowl. But it just keeps going.] In another bowl, stir together yogurt [lemon yogurt, you recall], rosemary, and parsley. Gently fold the yogurt mixture into the shrimp combination. Place one lettuce leaf and an avocado half on each serving plate. Fill the avocado halves with the shrimp and yogurt mixture. Top with ground pepper and serve.
A quick google reveals that shrimp stuffed avocado (made with lime and cilantro, and NO YOGURT, LEMON OR OTHERWISE) is a perfectly cromulent Colombian appetizer. This version, however, reminds me of that Sweet Valley Twins book wherein Jessica enters a pineapple-recipe contest to win a trip to Hawaii, but she can't bother to actually cook anything so she makes up a pineapple upside-down cake with, like, tuna and hot sauce or something. Then when she actually wins the trip she feels guilty the whole time.
AND it reminds me of another book I just read about cooking at the turn of the century, a period in which ambitious women who still couldn't get out of the kitchen did terrible things to food in the name of science and modern civilization. Monochromatic meals were the height of fashion and any food item could become a salad by the addition of mayonnaise or, even better, gelatin.
I guess what I'm trying to say is that the author of this recipe can only be a repressed Victorian female scientist trapped in the body of a lazy middle school student