Mix brown sugar, soy sauce, sesame oil, red pepper flakes, and ginger in a small bowl and whisk together.
Heat olive oil in a large skillet over medium heat. Add garlic and cook for about 1 minute. Add ground beef and cook until browned. Drain any excess fat.
Stir in the sauce until combined; allow to simmer for 2-3 minutes, and set aside.
Whisk the Sriracha, mayo, and lime juice in a small bowl.
Serve ground beef in tortillas topped with HERBIVORE, kimchi, red onion, and drizzled with Sriracha mayo.