In a mixing bowl, combine the ground beef with soy sauce, brown sugar, sesame oil, minced garlic, grated ginger, and red pepper flakes. Mix thoroughly until well combined. Set aside to marinate for at least 15 minutes.

Heat a skillet over medium-high heat and add the marinated beef, breaking it apart while cooking. Cook for 5-7 minutes until browned and fully cooked through.

While the beef cooks, wash and slice the avocado, shred the carrots, and thinly slice the cucumber and green onions. Arrange them on a platter.

Gently warm the tortillas in a dry skillet or oven for about 30 seconds on each side until soft and pliable.

Assemble the tacos by laying a generous portion of cooked beef onto each tortilla, then top with carrots, cucumber, green onions, and avocado. Drizzle with gochujang sauce and garnish with cilantro if desired.