In a large bowl, whisk together the orange juice, lime juice, garlic, chili powder, onion powder, paprika, salt, and pepper. Add the chicken thighs and turn to coat. Cover and let marinate in the refrigerator for at least 30 minutes or up to overnight.
Preheat the oven to 425°F with a rack in the center position. Line a rimmed sheet pan with foil. Set a metal cooling rack inside the prepared sheet. Place the marinated chicken on the cooling rack and roast the chicken for about 20 minutes, or until the internal temperature reads 165°F on an instant-read thermometer.
Transfer the chicken to a cutting board, rest for 5 minutes, then thinly slice.
Meanwhile, make the slaw. In a large bowl, combine the mangos, red onion, cabbage, cilantro, lime juice, and salt.
Divide the chicken evenly among the tortillas. Add the slaw, avocados, and salsa verde, if using. Serve the tacos with lime wedges for squeezing, if desired.