For the Marinated Chicken:
2 1/2 pounds boneless, skinless chicken thighs, cut into 1-inch chunks
2 tablespoons Asian fish sauce
1 tablespoon light brown sugar
1 tablespoon orange juice
For the Caramel Glaze:
2/3 cup packed light brown sugar
1/3 cup Asian fish sauce
1/3 cup orange juice
1/3 cup rice vinegar
2 tablespoons honey
4 medium cloves garlic, minced
2 medium shallots, chopped
1 (1-inch) piece peeled fresh ginger, minced
To Grill and Garnish:
1/4 cup white sesame seeds
1/4 cup black sesame seeds
1/3 cup sliced almonds
2 scallions, white and light green parts only, thinly sliced on a bias
For the Marinated Chicken: In a large zipper-lock bag, combine chicken, fish sauce, brown sugar, and orange juice. Shake well to coat. Refrigerate for at least 2 hours or up to overnight.
For the Caramel Glaze: In a medium saucepan, combine the brown sugar, fish sauce, orange juice, rice vinegar, and honey over medium heat. Stir until sugar dissolves. Add garlic, shallots, and ginger and continue to cook, stirring occasionally, until glaze becomes thick and sticky and easily coats the back of a spoon. Remove from heat and set aside.
To Grill and Garnish: Light one chimney full of charcoal. When all the charcoal is lit and covered with gray ash, pour out and spread the coals evenly over half of coal grate. Alternatively, set all the burners of a gas grill to high heat. Set cooking grate in place, cover grill, and allow to preheat for 5 minutes. Clean and oil the grilling grate.
Scatter white and black sesame seeds and almonds evenly all over a rimmed baking sheet.
Thread the chicken on 6 bamboo skewers. Transfer to the grill and cook over direct heat, turning and brushing with the glaze every 5 minutes until chicken is cooked through and crisp, about 8 minutes. When skewers are nearly done, brush chicken liberally one last time with glaze and roll the skewers in the sesame-almond mixture to coat. Return to grill and cook, turning, until almonds are lightly toasted, about 2 minutes. Remove from heat, garnish with scallions, and serve.