Whisk together soy sauce, brown sugar, sesame oil, rice vinegar, gochugaru, garlic, ginger, and Asian pear in a mixing bowl until sugar dissolves.
Add sliced beef to marinade, ensuring all pieces are coated. Cover and refrigerate for at least 2 hours or overnight for maximum flavor.
While beef marinates, make kimchi slaw: In another mixing bowl, combine shredded cabbage, chopped kimchi, sliced green onions, rice vinegar, and sesame oil. Refrigerate until ready to use.
Make gochujang mayo: Stir together mayonnaise, gochujang, lime juice, and honey until smooth. Refrigerate.
Heat grill or cast iron skillet over high heat until very hot (about 450°F if using a grill).
Remove beef from marinade and cook in batches 2-3 minutes per side until caramelized with some char. Don't overcrowd the pan.
Let beef rest for 5 minutes on cutting board, then slice against the grain into bite-sized pieces.
Warm tortillas on the grill or in a dry skillet for about 20 seconds per side.
Assemble tacos: Place warm tortillas on a plate, add Korean BBQ beef, top with kimchi slaw, drizzle with gochujang mayo, and garnish with sesame seeds and cilantro. Serve immediately with lime wedges.