In a small bowl, mix together the olive oil, garlic powder, oregano, basil, pepper, salt, onion powder, and Dijon mustard and pepperoncini juice.
Pour in the vinegar, and whisk until well blended. Reserve 1/4 c. of marinade for serving.
Place chicken thighs in a plastic storage bag and pour remaining marinade over chicken. Allow to marinate overnight or 8 hours. Once marinated, discard marinade. DO NOT CROSS CONTAMINATE.
Grill chicken in a grill pan over medium-high heat until the chicken is cooked through to 165 degrees.
Warm up tortillas in the microwave or in a dry skillet.
Top each tortilla with chicken, pickled onions, pepperoncini, olives, tomato, feta, reserved dressing and taziki. Say Grace and enjoy!