In a small saucepan, bring the brown sugar and water to a boil. Transfer to a large bowl. Whisk in the lime juice and chili-garlic sauce; let cool. Whisk in the oil and season with salt and pepper. Add the chicken, mango, avocado and scallions and toss thoroughly with the dressing. Add the mesclun and gently toss. Transfer the salad to plates and serve with lime wedges.