Slice fennel bulb into quarters lengthwise through the core. Cut out core; discard. Slice bulb lengthwise ¼" thick. Cook in a large saucepan of boiling salted water until just beginning to soften and turn translucent, about 2 minutes. Using a slotted spoon, transfer to a bowl of ice water and let cool. Drain; pat dry with paper towels.
Whisk together ginger, garlic, gochujang, vinegar, honey, oil, gochugaru, and sesame seeds in a medium bowl. Add fennel and toss to coat; season with salt.
Do Ahead: Fennel can be made 4 days ahead. Cover and chill.
