Step 1

Whisk lemon juice, miso, mustard, maple syrup, garlic, and 1 Tbsp. water in a small bowl to combine. Gradually add oil, whisking constantly until emulsified; set aside.

Step 2

Cook noodles in a large saucepan of boiling salted water according to package instructions until al dente. Drain; rinse under cold water, then drain again.

Step 3

Toss noodles, scallions, tofu, pea shoots, sugar snap peas, and radish in a large bowl with three-quarters of reserved dressing to combine and evenly coat; season with salt. Top with nori and horseradish and drizzle remaining dressing over.

Step 4

Do Ahead: Dressing can be made 1 day ahead. Cover and chill.