Slice flank steak against the grain.
In a bowl, mix together ingredients for the marinade. Add sliced beef and mix until coated. Let marinade in the fridge for 30 minutes.
Slice onion and spiralize zucchinis.
In a mixing bowl, add soy sauce, coconut sugar, ginger powder, chilli powder, garlic powder, cornstarch and water. Mix until combined.
Heat up 1 tbsp oil in a large nonstick skillet over medium heat. Add onion and stirfry for 1 minute.
Increase heat to high, add marinated beef and let sear until golden brown, about 1-2 minutes.
Remove beef from heat and transfer to a plate.
Reduce heat to medium and add the soy sauce mixture. Cook for 1-2 minutes or until it has thickened to the consistency of syrup. Add beef and spiralized zucchini to skillet and stir. Cook for 1 minute or until zucchini is cooked to desired doneness.
Remove from heat and serve immediately. Garnish with sesame seeds. Enjoy!