For the poppy seed dressing: Whisk sugar, rice vinegar, onion and mustard powder in a small bowl to blend. Gradually whisk in oil. Stir in poppy seeds. Season to taste with salt and pepper. (Can be made 1 week ahead. Cover and refrigerate.).
For the Asian Barbecue Sauce: Whisk hoisin sauce, oil, honey, soy sauce, ginger, garlic and crushed red pepper in a small bowl to blend. (Can be made 1 day ahead. Cover and chill.).
For the Croutons: Melt butter in a medium skillet over medium heat. Add garlic, basil and oregano and stir 1 minute. Add bread cubes and toss to coat. Sprinkle with salt and pepper. Saute until croutons are golden, about 12 minutes. Transfer to a plate to cool. (Can be made 3 hours ahead. Let stand at room temperature.).
For Salad: Prepare barbecue to medium high heat. Sprinkle chicken with salt and pepper; brush with oil. Grill chicken until cooked through, about 5 minutes per side. Brush chicken with some Asian barbecue sauce. Grill 1 minutes longer per side. Transfer chicken to work surface; let stand 5 minutes. Cut crosswise into 1/2-inch thick strips.
Place lettuce and croutons in large bowl. Toss with 1/2 cup dressing. Dived lettuce mixture among 4 plates. Garnish with tomatoes and grilled chicken strips. Drizzle chicken with barbecue sauce. Sprinkle with sesame seeds and serve.