In a blender, add tomatoes, cucumber, red pepper, celery, scallions, cilantro, parsley, vinegar, lemon juice, tomato juice, half of the avocado, 1/4 teaspoon black pepper and 1/4 teaspoon salt. Blend until it reaches desired consistency. Chill, covered, in refrigerator for at least one hour or overnight to let flavors meld.
Pat scallops dry and season with remaining 1/4 teaspoon black pepper and 1/4 teaspoon salt. Heat oil in a nonstick skillet over high heat. Add scallops and sear about 2 minutes per side (or to desired doneness), until scallops are no longer translucent.
Chop remaining half of avocado. To serve, divide gazpacho between 4 bosl and top with scallops and avocado slices.