In a large skillet over medium-high 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, gochujang, sesame oil, garlic, ginger, and erythritol. Cook for an additional 3-4 minutes until the beef is well coated and heated through. Season with salt and pepper to taste.
In a separate bowl, combine the sliced cucumber, rice vinegar, sesame seeds, and chopped green onions. Toss to coat evenly.
Serve the spicy beef hot, alongside the cucumber salad for a refreshing contrast.