Mix up sauce in a small bowl or jar and set aside.
Chop up all your veggies so they're ready to cook.
Soak sweet potato noodles in a large bowl of warm water for 20 minutes. Strain and rinse soaked noodles. Bring a large pot of water to a boil, then add soaked sweet potato noodles and cook for 5 minutes (until they are clear and tender). Strain. Do not rinse. Set aside.
While sweet potatoes are soaking/cooking, you will be cooking the vegetables.
Start with a large skillet with 1/4 cup of water and cook the onions and mushrooms until the onions are translucent. The water should fully cook off.
Set onions/mushrooms aside on a dinner-size plate.
Now, add the carrots and red bell peppers into the skillet with 1/4 cup water and cook until tender-crisp. The water should fully cook off.
Set carrots/peppers aside on the plate where you placed the onions/mushrooms.
Finally, place the spinach in the skillet with a few tablespoons of water and cook just until wilted. Drain off excess moisture and place spinach on dinner plate with the rest of the veggies.
In a large bowl, place the sweet potato noodles. Pour the sauce over the noodles and mix well with a tongs or a plastic-gloved hand. Add in the veggies and toss well. Add sesame seeds.
Serve in bowls with extra toasted sesame seeds for garnish.