1. Combine 1 tablespoon oil, cider vinegar, minced shallots, and Dijon mustard in a large bowl, stirring with a whisk. Add salad greens, halved cherry tomatoes, and cucumber to bowl; toss gently to coat.
2. Heat a large nonstick skillet over medium-high heat. Add sliced prosciutto to pan; cook 3 minutes or until prosciutto is crisp; coarsely chop. Pat scallops dry with paper towels; sprinkle with freshly ground black pepper and kosher salt. Add remaining 2 teaspoons olive oil to pan; swirl to coat pan. Add scallops to pan; cook 3 minutes on each side or until desired degree of doneness. Place 4 scallops and 2/3 cup salad mixture on each of 4 plates; sprinkle with prosciutto.