In a saucepan on low heat, combine water, white sugar, fish sauce and rice vinegar. Heat through, stirring, until sugar is dissolved. Add garlic. Taste and adjust seasoning as desired and keep warm.
Divide lettuce between bowls.
Bring a large pot of water to a boil. Cook vermicelli according to package instructions. Drain, place on top of lettuce.
Meanwhile, heat vegetable oil and Sambal Oelek in a skillet over medium heat. Add shrimp and cook until opaque, 2 to 3 minutes.
Top vermicelli with shrimp, cucumber, carrot, green onions and peanuts.
Divide sauce into individual bowls.
Serve immediately with soy sauce, Sriracha, and chili oil to taste.