Whisk sauce ingredients together in a medium bowl and set aside.
Heat oil in large pan. Add the green onions and sauté for 1-2 minutes, then add broccoli, carrots, and red bell pepper. Lower heat, if needed. Cook until vegetables are bright in color, and just barely tender.
Toss gently to coat the veggies with the sauce. Let simmer to thicken the sauce.
Remove from heat and serve immediately on top of the spiralized zucchini. Garnish with red pepper flakes and sesame seeds, if desired.
Notes
The sauce and veggies can be made ahead, and the zucchini can be spiralized ahead. But don’t combine with the “zoodles” until right before serving. Otherwise, the liquid from the zucchini will seep out and make the sauce watery.