Add frozen yuca to boiling water. Bring back to a simmer, cover with a lid, and let yuca cook for 20 minutes until it is soft. Remove the hard inner "spine" (hard, twig-like string in the center of the yuca).
In a pan, sauté onion slices in olive oil for 3 minutes. Add minced garlic, orange juice, lemon juice, lime juice, and some salt. Fry for 5-7 minutes.
Transfer soft yuca wedges to a plate or bowl. Pour garlic sauce over yuca. Sprinkle with cilantro and add salt and pepper for taste. Serve immediately.
Leftovers will keep in an airtight container in the refrigerator for 3-4 days.