Place the sliced cucumbers and red onion in a medium bowl. Add the apple cider vinegar, 1 tablespoon sugar-free sweetener, salt, black pepper, and 1 teaspoon sesame seeds if using. Toss well, gently massage the cucumbers to coat, and set aside to marinate.

Heat a large skillet over medium high heat. Add the ground beef and cook for 5 to 7 minutes, breaking it up with a spatula, until browned and no longer pink. Drain excess fat from the skillet if needed.

Add the sesame oil and minced garlic to the beef and cook for 30 seconds, stirring. Stir in the soy sauce or coconut aminos, 2 tablespoons sugar-free sweetener, rice vinegar, crushed red pepper flakes, and ground ginger.

Reduce the heat to medium and simmer the beef mixture for 2 to 3 minutes, stirring, until the sauce slightly thickens and coats the meat.

Remove the skillet from the heat. Stir in half of the sliced green onions and half of the sesame seeds. Taste and adjust salt or heat if needed.

Divide the spicy Korean ground beef among four plates. Top with the remaining green onions and remaining sesame seeds.

Serve the cucumber salad on the side with each portion of beef, garnishing with extra sesame seeds if desired.