In a large container or a large zipper-top bag, combine the soy sauce, oil, garlic, ginger, and red pepper flakes. Add the chicken breasts, turn to coat, and marinate in the fridge for at least 2 hours and up to 8, with the container covered or the bag sealed.
Preheat the grill to medium-high (or heat a grill pan lightly brushed with oil over medium-high heat on the stove). Grill or pan-grill the chicken for about 5 minutes on each side, until just cooked through. You can flip the chicken once for simple grill marks, or turn it a quarter turn after you flip it, turning the chicken every 2 minutes or so, and get those nice cross-hatched grill marks.
Let the chicken sit for a few minutes, then slice and serve.
Notes
If you prefer to make this with boneless skinless chicken thighs, just up the cooking time to about 7 minutes on each side.