Heat 1 tablespoon sesame oil in a large skillet over medium-high heat. Add mushrooms and snow peas and saute until tender, about 3-5 minutes. Transfer to a bowl and keep warm.
In a small bowl, whisk miso, water, vinegar, agave, soy sauce, sweet chili sauce, and red pepper flakes until smooth.
Heat remaining 1 tablespoon sesame oil in same skillet over medium heat. Add scallions and garlic and saute 2-3 minutes until fragrant. Add miso sauce and bring to a low simmer. Remove from heat, cover, and set aside.
Cook udon noodles according to package instructions to al dente. Drain noodles, rinse well, and immediately add to miso sauce, folding until evenly coated.
Season noodles with salt and pepper to taste if needed and serve alongside sauteed mushrooms and snow peas. Enjoy!