Preheat the oven to 350˚F.
Place the chicken breast in a zip top bag, or covered container. Add the lime juice, orange juice, jalapeño slices, garlic, oregano, cumin, salt, pepper, and half of the cooking oil. Mix well.
Let marinate in the refrigerator for at least 20 minutes, or up to 3 hours.
Heat the remaining cooking oil in a large oven-safe skillet over medium high heat.
Once hot, add the chicken breast to the skillet and let sit on the first side for 2-3 minutes without moving.
Once a nice golden brown sear has formed, flip the chicken and cook an additional 2-3 minutes.
Transfer the skillet to the oven and cook for an additional 10-15 minutes or until chicken reaches 165˚F internal temperature.
Let sit for 5 minutes, then dice the chicken.
Place all sauce ingredients in a blender or food processor and blend until smooth.
Heat a little cooking oil in a skillet over high heat. Once hot, add a tortilla and cook on each side for 30-45 seconds until lightly browned.
Repeat with all tortillas to create the taco shells.
Assemble the tacos by layering a taco shell with chicken, pickled onions, tomatoes, feta, cilantro sauce, and top with smashed avocado and fresh cilantro.
