A refreshing starter
Brush 2 teaspoons lemon juice over flesh of avocados; set aside.
Remove peel and pith from grapefruit using sharp paring knife. Working over medium bowl to catch the juice, carefully carve out segments from between membranes. Transfer grapefruit segments to a small bowl; set aside. Reserve juice in bowl.
Add ¼ cup lemon juice, the salt, and tarragon to the grapefruit juice; season with pepper. Whisk in oil in a steady stream. Add grapefruit sections; toss gently just to coat.
Place each avocado half on a plate. Top with grapefruit mixture, dividing evenly. Garnish with tarragon. Serve with lime wedges.