Grilled Scallops with Spring Greens

Name: Grilled Scallops with Spring Greens
Ingredients: Nonstick cooking spray; 12 large sea scallops; Kosher salt and freshly ground black pepper; 1/2 teaspoon herbed Dijon mustard; 1 teaspoon sherry vinegar; 1 teaspoon fresh lemon juice; 1 tablespoon extra-virgin olive oil; 1 teaspoon walnut oil; 1 teaspoon boiling water; 4 cups mixed greens (baby spinach, arugula, mache); 1/4 cup coarsely chopped basil leaves; 1 teaspoon chopped fresh tarragon; Four 6-inch bamboo skewers, soaked in water