In a medium bowl, whisk together mayo, Greek yogurt, and minced shallot until smooth. Stir in chopped parsley, chopped cilantro, minced garlic, extra virgin olive oil, red wine vinegar, and kosher salt. Adjust seasoning if needed, then set aside.

Combine garlic powder, kosher salt, and black pepper in a small bowl. Pat chicken breast dry and rub seasoning mix evenly over the chicken. Let it sit for about 10 minutes.

Heat avocado oil in a skillet over medium heat. Add seasoned chicken breasts and cook for 4-5 minutes on each side until the internal temperature reaches 165°F. Transfer to a plate to rest before shredding.

In the same skillet, add a splash of water to deglaze. Add jalapeño and red onion; sauté for 3-4 minutes until tender and fragrant.

Return shredded chicken to the skillet with sautéed veggies. Add chopped cilantro, mix well, and cook for an additional 1-2 minutes until heated through.

Warm flour tortillas in a dry skillet for about 30 seconds each side. Assemble each with shredded romaine, chicken mixture, sliced avocado, and crumbled feta cheese. Drizzle with chimichurri sauce and serve warm.