Reduce heat to medium, and add remaining tablespoon oil to skillet. Add garlic, and cook for 15 seconds. Add spinach, arugula, red-pepper flakes, and remaining 1/2 teaspoon salt and 1/8 teaspoon pepper. Cook, tossing greens often, until just wilted, about 2 minutes. Transfer to a platter, top with scallops, and serve immediately.