Thaw scallops, if frozen. Rinse scallops; pat dry with paper towels. Set aside.
Using a sharp knife, score lemon into 4 lengthwise sections; remove peel from lemon. Scrape white portion from peel; discard. Cut peel into very thin strips; set aside. Squeeze enough juice from lemon to measure 2 tablespoons; set aside.
In a large skillet cook asparagus and onion in 1 tablespoon of the hot oil over medium-high heat for 2 to 3 minutes or until crisp-tender, stirring frequently. Sprinkle with salt and black pepper. Transfer asparagus mixture to a serving platter. Cover and keep warm.
In the same skillet combine the reserved lemon peel strips, the remaining 2 tablespoons olive oil, and the basil sprigs. Cook for 30 to 60 seconds or until heated through. Using a slotted spoon, remove lemon peel and basil sprigs, reserving oil in skillet. Discard lemon peel and basil sprigs.