Whisk together Greek yogurt, mayonnaise, shallot, parsley, cilantro, olive oil, red wine vinegar, and garlic in a bowl. Adjust seasoning with salt as needed.

Combine garlic powder, salt, and black pepper in a bowl. Rub this mixture evenly over chicken breast and let sit for about 10 minutes.

Heat olive oil in a skillet over medium-high heat. Add chicken breast, sear for 4-5 minutes on each side until browned and cooked through. Let rest before shredding.

In the same skillet, add diced jalapeño and red onion, sauté for 3-4 minutes until tender and caramelized.

Combine shredded chicken with sautéed vegetables and add cilantro. Mix everything together.

Warm tortillas and layer with lettuce, avocado, chicken mixture, and feta cheese. Drizzle with chimichurri sauce before serving.