Prepare dressing: In a small bowl, combine yogurt, milk, mint, dill, garlic, salt and pepper. Store, covered, in refrigerator while preparing shrimp.
Prepare salad: Thaw shrimp, if frozen. Peel and devein shrimp. Rinse shrimp; pat dry with paper towels. Thread shrimp onto four 12-inch skewers, leaving ¼-inch space between each shrimp (see Tip). Sprinkle shrimp with the salt and pepper.
For a charcoal grill, place shrimp skewers on the grill rack directly over medium coals. Grill, uncovered, for 6 to 8 minutes or until shrimp are opaque, turning once halfway through grilling. (For a gas grill, preheat grill. Reduce heat to medium. Place skewers on grill rack over heat. Cover and grill as above.)
To serve, divide salad greens among four serving plates. Top with cucumber, jicama and radishes. Top each salad with a shrimp skewer. Spoon dressing over salads. If desired, sprinkle with goat cheese. Serve immediately.
Tips: Use a vegetable peeler to shave enough wide strips of the peeled jicama to make ½ cup.
If using wooden skewers, soak in enough water to cover for at least 30 minutes before grilling.