In a medium bowl, whisk together Greek yogurt, mayonnaise, minced shallot, chopped parsley, and chopped cilantro. Add avocado oil, red wine vinegar, minced garlic cloves, and a pinch of salt until smooth. Set aside.

Season chicken breasts with garlic powder, salt, and pepper. Let sit at room temperature for 10 minutes.

Heat avocado oil in a skillet over medium heat, then cook the seasoned chicken for 4-5 minutes on each side until golden and cooked through. Transfer to a cutting board to rest.

In the same skillet, add a splash of water, then sauté sliced jalapeño and onion for 3-4 minutes until softened.

Return shredded chicken to skillet, add chopped cilantro, and mix well. Remove from heat.

Warm tortillas, layer with lettuce, avocado, and chicken mixture, then top with feta cheese and chimichurri sauce. Serve immediately.