1. Coat mushrooms, bell pepper, and onion with cooking spray.
2. Grill onion in a WEBER Charcoal or Gas Barbecue, covered with grill lid, over medium-high heat (350 degrees to 400 degrees) 8 minutes on each side. Grill mushrooms 5 minutes on each side. Place bell pepper skin side down and grill for 4 to 5 minutes.
3. Peel bell peppers and cut into strips.
4. Spread avocado mayonnaise on cut sides of buns; place on cooking grate, and grill 1 minute.
5. Place mushrooms, bell pepper strips, and onion evenly on bottom halves of buns.
6. Top evenly with avocado slices and bun halves.
7. Makes 6 servings
8. Avocado Mayonnaise:
9. 1 small California avocado, peeled and chopped
10. 1/2 cup mayonnaise
11. 2 tablespoons lemon juice
12. 1/4 cup fresh basil leaves
13. 1 garlic clove, minced
14. Process all ingredients in a food processor until smooth, stopping to scrape down sides. Cover and chill 2 hours, if desired.

*Large avocados are recommended for this recipe. A large avocado averages about 8 ounces. If using smaller or larger size avocados adjust the quantity accordingly.