Heat the olive oil in a small saucepan over medium heat. Stir in the sesame seeds and cook until lightly browned, about 3 minutes. Scrape into a metal mixing bowl and cool to room temperature.
Whisk the vinegar, teriyaki sauce, black pepper, crushed chillies, ginger and sweetener into the sesame seed mixture. Stir in the celery, spring onions, carrots, pepper, cucumber and onion into the sesame dressing until evenly coated. Cover and refrigerate until cold before serving.