Bring a large pot of water to boil and cook the noodles according to package directions. Drain and rinse with cold water, then return to the pot. While you are waiting on the water to boil, prep the veggies as described above.
In a medium bowl, whisk together the dressing ingredients (peanut butter, rice vinegar, sesame oil, soy sauce, honey, ginger, and garlic) until smooth. The mixture should be thick but pourable. if it’s too thick, you can whisk in water in 1 tablespoon increments until you have achieved the right consistency. Taste and season with salt if needed.
In a large bowl, combine the cooked soba noodles, slaw mix, shredded brussels sprouts, and chopped green onions. Pour dressing over the vegetables and toss to coat. This slaw keeps well for about 3 days (covered and refrigerated).