1. Preheat oven to 425°. Snap off and discard tough ends of asparagus; remove scales with a vegetable peeler, if desired.
2. Stir together 1 Tbsp. olive oil, 1 1/2 tsp. chopped basil, 1/2 tsp. lemon pepper, and 1/4 tsp. salt in a large bowl.
3. Add asparagus to olive oil mixture, and toss gently to coat. Place asparagus on a lightly greased baking sheet.
4. Bake asparagus at 425° for 13 to 15 minutes or to desired degree of tenderness. Cool 10 minutes.
5. Whisk together balsamic vinegar, garlic, and remaining 7 Tbsp. olive oil, 1 Tbsp. basil, and 1/4 tsp. salt.
6. Toss together tomatoes, bell pepper, onion, and 1 Tbsp. balsamic vinegar mixture.
7. Arrange lettuce on individual serving plates. Top with tomato mixture and asparagus. Add avocado just before serving. Drizzle with remaining balsamic vinegar mixture.
Note: To make ahead, toss together tomatoes, bell pepper, and onion without dressing. Store these ready-to-use ingredients in an airtight container in the refrigerator up to five hours. The dressing and asparagus can also be made up to eight hours before serving.