Grill or pan-sear until caramelized and cooked through. Set aside to rest.
Boil udon as directed. In the last 2 minutes, toss in chopped asparagus.
Drain, then stir in spinach to wilt from residual heat.
Toss noodles + greens with a drizzle of sesame oil, a spoon of teriyaki, and a pinch of chilli flakes.