Pat the squid very dry. Score the inside of each body in a light crosshatch if you have the patience, then cut into 2 cm rings. Wet squid steams instead of searing, so drying it is the single most important step.
Stir the gochujang, gochugaru, soy sauce, sugar, rice wine, garlic and ginger together in a small bowl until smooth.
Heat the neutral oil in a wok or large skillet over high until it just starts to shimmer. Add the onion, carrot and cabbage and stir fry 2 to 3 minutes, until the cabbage is wilted but still has bite.
Push the vegetables to the side and add the squid in a single layer. Sear 1 minute without touching it, then toss for another 1 to 2 minutes until the squid is just opaque and curled. Squid is done in about 3 minutes total, so move fast.
Pour in the sauce and toss everything for 1 to 2 minutes, until the squid and vegetables are coated and the sauce turns glossy. Pull it off the heat the moment the squid firms up.
Stir through the scallions and sesame oil off the heat. Top with sesame seeds and serve hot over rice.