Mix brown sugar, tamari and brown rice vinegar in a bowl. Either let sit or whisk until sugar dissolves. (If you are in a hurry, you can heat the tamari and brown rice vinegar until warm, pour over the sugar, and the sugar will dissolve faster.)
Heat sesame oil in a pan and add serrano pepper and mixed vegetables. Cook until crisp tender. Add garlic, ginger, and brown sugar mixture. Cook for 30 seconds more.
Add zucchini and carrot noodles. Cook until tender.