In a small to medium saute pan, heat oil and add all chopped zucchini and onions at the same time.
When it starts to sizzle lower heat to a medium. Cook until zucchini is fork tender but not too mushy about 7-10 minutes. Add soy sauce in the last minute or two of cooking so it can evaporate a bit. Mix frequently while cooking.
Add a dash of sesame seeds right before serving.
Notes
Be careful to not overcook the zucchini because it will turn mushy. Better to undercook than overcook.