In a large skillet over medium heat, add the ground beef. Cook until browned, breaking it apart with a spatula, about 5-7 minutes. Drain excess fat if necessary.
Stir in the soy sauce, sesame oil, gochujang, brown sugar, garlic, ginger, rice vinegar, and black pepper. Cook for an additional 3-5 minutes, allowing the flavors to meld.
While the beef is cooking, prepare the cucumber salad. In a bowl, combine the sliced cucumber, green onions, and sesame seeds. Toss gently to mix.
Serve the spicy ground beef over a bed of cucumber salad. Garnish with additional sesame seeds if desired.