Slice chicken breasts into even strips about ½-inch thick. In a large bowl, toss the chicken with olive oil, oregano, garlic powder, salt, and pepper until every piece is coated. Let marinate while you prep the vegetables.

Cut bell peppers into strips and slice the red onion into crescents, keeping them roughly the same size as your chicken. Slice the zucchini into half-moons about ¼-inch thick.

Heat a large cast-iron skillet or heavy pan over medium-high heat until hot. Add the marinated chicken strips in a single layer, avoiding overcrowding. Cook for 4-5 minutes without moving them, then flip and cook another 3-4 minutes until internal temperature reaches 165°F.

Remove the chicken to a plate and add sliced vegetables to the same pan with the basil and olive oil. Sauté for 6-8 minutes, stirring occasionally, until peppers develop slight char marks and onions become translucent with golden edges.

Return the chicken to the pan with the vegetables for the final minute, tossing everything together. Warm tortillas and fill each one with the chicken and vegetable mixture. Top with crumbled feta, tzatziki, fresh parsley, and a squeeze of lemon juice.