1.Spray a large frying pan with oil; heat on high. Grill chicken, in batches, 2-3 minutes each side, until browned and cooked through. Set aside.
2.Using same pan, cook bacon 3-4 minutes each side, or until crisp. Drain on paper towel; tear into small pieces.
3.To make mayonnaise: place garlic, basil, egg and lemon juice in food processor; pulse to combine. With motor running on medium speed, add oil in a slow stream. Blend until thick. Season to taste.
4.Top toasted bread with lettuce, chicken, tomato and bacon. Season to taste and drizzle with mayonnaise. Serve topped with green onion.