If your prawns are frozen, defrost them in the microwave and pat dry with paper towels.
Follow the preparation instructions for the noodles.
Cut cucumber in quarters lengthwise and remove seeds with your knife. Cut cucumber in matchsticks.
Peel and cut carrot in matchsticks.
Roughly tear herbs with your hands.
Place water, fish sauce, vinegar, lime juice, sweetener and garlic powder in a small bowl and whisk until sweetener is dissolved. Add chilli if using.
Serve vermicelli at the bottom of a bowl. Arrange vegetables, prawns and herbs on top, pour dressing on top of everything. Garnish with peanuts, chilli slices and a lime wedge.