Prepare barley according to package directions (you should have approximately 3 cups when cooked).
Light a grill over medium heat. Skewer the asparagus tips, mushrooms, tomatoes and onion chunks. Lightly brush with olive oil. Place on grill and cook 5 minutes on each side, or until lightly browned around edges. Remove veggies from skewers and place into a medium bowl. Cover to keep warm.
In a medium bowl, combine sea scallops, olive oil, garlic, seasonings and lemon juice. Gently stir until scallops are well coated. Place heavy duty aluminum foil on the grill and fold up the edges. Transfer scallops to foil in a single layer and pour remaining liquid over top. Cook scallops for 3 minutes per side, or until cooked through (be careful not to over-cook!). Remove from grill.
Layer each plate as follows: 3 large spoonfuls cooked barley, 1/4 of the grilled veggies, 5-6 grilled scallops and 2-3 avocado slices. Drizzle liquid from aluminum foil over the tops. Serve immediately!