Heat oil in a wok or large heavy based skillet over high heat.
Add garlic and ginger, stir for 10 seconds. Add onion, stir for 30 seconds.
Add carrot, capsicum and stems of buk choy - stir for 1 minute.
Add mushrooms, then stir for 2 to 3 minutes until the vegetables are almost cooked.
Add Sauce and toss for 1 minute until Sauce thickens and becomes glossy, coating all the vegetables. Don't overcook so they become floppy and limp - they should be just cooked, “crisp tender”.
Remove from stove and serve over rice (low carb option: cauliflower rice). Garnish with green onions and sesame seeds if using.