Preheat oven to 425ºF (220ºC). Line a baking sheet with foil and lightly spray with vegetable oil.
To make the sauce: In a bowl, combine the coconut milk, stock, lemon juice, hoisin, sugar, cornstarch, ginger, garlic and Sriracha and stir until the cornstarch is dissolved. Set aside.
To make the meatballs: In a bowl, combine the beef, egg, hoisin, onions, breadcrumbs, cilantro, garlic, ginger, and salt and pepper. Using your hands, form about thirty 1-inch (2.5 cm) meatballs. Place on the prepared baking sheet and bake in the preheated oven for 10 minutes or until internal temperature reaches 165º (74ºC) when tested with a cooking thermometer.
In a small skillet over medium heat, cook the prepared sauce until slightly thickened, about 2 minutes.
Meanwhile, in a saucepan of boiling water, cook the noodles according to the package instructions. Drain well.
Top each lettuce leaf with an equal amount of the cooked noodles. Top noodles with 3 meatballs and drizzle with the sauce. Garnish with red pepper, sesame seeds or peanuts if you like.