In a small bowl, combine Greek yogurt, mayonnaise, minced shallot, parsley, cilantro, olive oil, vinegar, garlic, and salt. Whisk until smooth and set aside.

Season chicken breast with garlic powder, kosher salt, and black pepper. Let sit for 10 minutes.

Heat avocado oil in a skillet over medium heat. Cook chicken for 4-5 minutes on each side until internal temperature is 165°F. Let rest, then shred.

In the same pan, add jalapeño and red onion. Sauté for 3-4 minutes until softened.

Mix shredded chicken into the pan with the sautéed jalapeños and onions, folding in chopped cilantro.

Warm tortillas in a skillet. Layer with shredded lettuce, avocado, and the chicken mixture. Top with feta and drizzle chimichurri sauce.