Preheat grill to high. Combine chickpeas, garlic, celery, and 1/3 cup parsley with 2 tablespoons lemon juice and 1 tablespoon oil. Drizzle scallops with 2 teaspoons oil and 1 tablespoon juice. Toss and season with salt and pepper. Grill scallops 2 to 3 minutes per side, or until firm to the touch. Toss spinach with 1 tablespoon each of juice and olive oil; top with chickpea mixture and scallops.