Heat vegetable oil in a large skillet over medium-high heat. Add ground beef and cook, breaking up, until mostly browned.
Stir in garlic and ginger; cook 30 seconds until fragrant. Mix gochujang, soy sauce, brown sugar, sesame oil, and rice vinegar in a small bowl.
Pour sauce into skillet and simmer 2–3 minutes until beef is evenly coated and sauce slightly thickens. Taste and adjust sweetness or heat.
Serve over warm rice, top with green onions, cucumber slices, sesame seeds, and red pepper flakes.