In a mixing bowl, whisk together Greek yogurt and mayonnaise until smooth. Add minced shallot, chopped parsley, cilantro, olive oil, red wine vinegar, and minced garlic. Season with salt and set aside.

Season chicken breast with garlic powder, salt, and black pepper. Heat oil in a skillet over medium heat. Cook the chicken for 4-5 minutes per side until golden brown and fully cooked.

In the same skillet, sauté chalapeños and red onions for 3-4 minutes until softened. Deglaze with a splash of water.

Return shredded chicken to the skillet, mix in chopped cilantro, and cook for an additional 2-3 minutes.

Warm tortillas, layer with shredded lettuce, slices of avocado, and chicken mixture. Sprinkle with feta cheese and drizzle with chimichurri sauce. Serve immediately.