Pound chicken thighs, if desired. Combine soy sauce, vegetable oil, chile paste, sesame oil, garlic, ginger, and red chile flakes in a large owl. Whisk to completely dissolve chile paste. Add chicken and stir to coat. Cover with plastic wrap and refrigerate at least 30 minutes and up to 2 hours.
Preheat grill for medium heat and lightly oil the grate.
Grill the chicken until slightly charred and no longer pink in the center, 5 to 8 minutes per side. An instant-read thermometer inserted into the center should read at least 165 degrees F (74 degrees C).