Mix sugar and dry seasonings in a small bowl. In a 2-cup measuring cup, mix peanut sauce, coconut milk and broth. Split each breast by cutting in half horizontally. Lightly pound to about a 1/2-inch thickness. Place chicken and oil in a medium bowl; toss to coat. Sprinkle seasoning mix evenly over chicken breasts.
Heat a 12-inch non-stick skillet over medium-high heat until very hot, then add chicken. Cook, turning once, until crusty brown and fully cooked, about 2 minutes per side. Transfer to a cutting board and let rest.
Add peanut mixture to empty skillet; cook, stirring constantly to loosen brown bits, until sauce reduces by half, about 2 to 4 minutes. Return to measuring cup. (Chicken and sauce can be made 2 hours ahead; reheat in a warm oven or microwave.)
To serve, cut each breast cutlet into 12 to 15 bite-sized pieces. Transfer to a serving platter. Drizzle with a little peanut sauce, then sprinkle with peanuts and scallions. Serve immediately with toothpicks and remaining dipping sauce.
