In a medium bowl, combine garlic cloves, soy sauce, sugar, sesame oil, crushed red pepper, ginger, and ground pepper.
Add pork tenderloin and onion wedges; marinate at least 10 minutes.
In a 12-inch skillet, heat olive oil over medium heat. In three batches, brown pork and onion, 3 to 5 minutes per batch. Discard marinade.
Return all pork and onion to skillet; cook until warm. Garnish with toasted sesame seeds, if desired.