Gather collard leaves and roll into a log-shaped bundle; slice bundle crosswise into thin strips.
Bring a large pot of salted water to a boil. Add collard greens; simmer until bright green, about 10 minutes. Drain.
Heat olive oil in a large skillet over medium heat. Add bacon; cook and stir until browned, about 5 minutes. Stir in drained collard greens, onion, sea salt, and garlic; cook until flavors combine, about 10 minutes.