Preheat your oven to 400F and line a baking sheet with parchment.
Break the head of broccoli down into bite-sized florets and pieces.
Transfer the florets and pieces to the baking sheet. Drizzle the avocado oil over the broccoli and use your hands to mix it all up, coating the broccoli well with the oil. Sprinkle the broccoli with the red pepper flakes and a pinch of the kosher salt.
Roast the broccoli for 25-30 minutes, or until it's browning and crispy.
10 minutes (or so) before the broccoli is ready, bring a pot of water to boil. Cook the soba noodles according to package instructions, then drain.
Transfer the roasted broccoli, noodles, purple cabbage, and kimchi to a large mixing bowl.
Whisk together the sesame oil, tamari, and rice vinegar together. Add the mixture to the noodles. Toss everything together till it's all mixed well. Taste and adjust tamari and vinegar as needed.
Top the noodles with sesame seeds, if using, and serve.
