For the glaze: In a small bowl, mix the gochujang, honey, a few grinds of black pepper and a pinch of salt, adding a splash of water if needed to loosen to a glaze consistency.
For the marinated veggies: In a bowl, toss together the rice wine vinegar, sesame seeds, chile flakes, scallions and carrots. Rest for 30 minutes at room temperature.
For the hot dogs and onions: In a grill pan on medium heat (or on the grates of a grill on high heat), add the onions and a drizzle of olive oil. Brush the onions with the glaze and cook, moving them around, until charred and golden, 5 to 8 minutes. Transfer to a cutting board and give them a rough chop. Cover with aluminum foil.
Add the hot dogs to the grill pan cut-side down and cook, flipping once, until heated through. On the flip, generously brush the cut side with the glaze. Remove from the grill and let rest with the onions under the foil.
Dry toast the buns on each side. Add the onions to the buns first, then the hot dogs and some of the marinated vegetables.