Prep: 20 minutes; Cook: 4 minutes.
Preheat grill or grill pan to medium-high.
Toss shrimp with 2 teaspoons olive oil. Stir in 1/4 teaspoon salt and 1/4 teaspoon pepper. Lightly spray grill or grill pan with olive oil spray, and cook shrimp about 2 minutes per side or until just cooked through. Transfer shrimp to a plate to cool.
In a small bowl, whisk together lime juice, honey, remaining 1/2 teaspoon salt, and more pepper to taste. Whisk in remaining 1 tablespoon olive oil.
In a medium bowl, combine red onion and 2 tablespoons mint. Add dressing, and toss gently. To serve, place 1 cup arugula on each of 4 plates and top with 2 melon wedges and 1/4 of the onion-mint mixture; sprinkle with equal amounts of feta, top with about 6 shrimp, and garnish with some of the remaining fresh mint. Serve immediately.