In a medium bowl, whisk together Greek yogurt, mayonnaise, minced shallot, parsley, cilantro, olive oil, red wine vinegar, garlic, and kosher salt until smooth. Set it aside.

In a small bowl, combine garlic powder, salt, and black pepper. Coat the chicken breast with this seasoning blend and let rest for 10 minutes.

Heat avocado oil in a skillet over medium heat. Cook the seasoned chicken breast for 4-5 minutes on each side until golden brown and cooked through. Let rest, then shred.

Deglaze the skillet with a splash of water, add jalapeño and red onion, and sauté for about 3-4 minutes until softened.

Return the shredded chicken to the skillet, mix in jalapeños and onions with cilantro until heated through.

Warm tortillas in a skillet, assemble tacos with lettuce, chicken mixture, and feta cheese, then drizzle with chimichurri sauce. Serve warm.