In a large bowl, combine the soy sauce, sesame oil, ginger, red pepper flakes, scallions and garlic. Stir to combine. Place the chicken into the marinade and stir to coat. Cover and place into the fridge for at least 6 hours, up to 24.
When ready to cook, remove the chicken from the fridge. Place a large skillet on the cooktop, add the oil and warm over medium heat. Once the pan is hot, add the shallots and cook until softened, about 3 minutes.
Add the orzo to the skillet, stir to coat and let toast for about 1 minute. Add the chicken and stir to coat.
Add the chicken stock to the skillet and turn the heat to medium-high. Once boiling, reduce the heat and let simmer for 15 minutes, or until the chicken is cooked through and the pasta is al dente. If the pasta is appearing dry, add additional chicken stock or water as needed.
Turn the heat to low and stir in the vinegar. Serve warm.