In a large bowl, combine the grated onion, minced garlic, orange juice, lime juice, ancho chili powder, garlic powder, cumin, dried oregano, paprika, cilantro, and salt.

Add chicken thighs to marinade and toss to thoroughly coat. Cover tightly with plastic wrap and refrigerate for at least 1 hour, or up to overnight. If short on time, leave uncovered on the counter for 15 minutes.

Remove chicken from fridge at least 30 minutes before grilling.

Preheat a gas grill to medium-high heat (450ºF). Clean and oil the grill grates.

Place the chicken thighs directly on the grill. Cover and grill until grill marks appear and the chicken does not stick, about 4-5 minutes. Flip and cook until grill marks appear on the second side, about 5 minutes more. Flip again and cook until an instant-read thermometer reads 170°-175ºF (or 165ºF for chicken breasts).

Transfer chicken to a cutting board and let rest for 4-5 minutes. Slice chicken into strips, then chop into 1/2-inch cubes.

Heat the tortillas on the grill for about 1 minute per side, or in a hot skillet for about 1 minute per side.

Stack 2 warm mini corn tortillas and top with chopped chicken, sprinkle with diced white onion and chopped cilantro. Serve warm with lime wedges.