In a mixing bowl, combine olive oil, balsamic vinegar, soy sauce, minced garlic, oregano, paprika, salt, and black pepper. Whisk until well combined to make a marinade.
Place the chicken thighs in a large zip-top bag or a shallow dish. Pour the marinade over the chicken, ensuring all pieces are well coated. Seal the bag or cover the dish and refrigerate for at least 30 minutes, or up to 4 hours for extra flavor.
Preheat the grill to medium-high heat (about 375°F to 400°F). If using a grill pan, heat it over medium heat on the stovetop.
Remove the chicken from the marinade and let excess marinade drip off. Discard the marinade.
Place chicken thighs, skin-side down, on the grill. Grill for 6-8 minutes on each side, or until the chicken reaches an internal temperature of 165°F (use an instant-read thermometer).
Once cooked, remove from the grill and let the chicken rest for 5 minutes before serving. Garnish with fresh herbs if desired.