Cook the rice as directed on the package.

In a small bowl, combine the vinegar, fish sauce, sugar, garlic, lime juice, and red pepper flakes. Reserve.

Preheat a large cast-iron pan over medium-high heat for 5 minutes. Lightly spray the shrimp and cut sides of the lettuce with the cooking spray and season with salt and pepper. Char the lettuce, cut side down, in the pan until the leaves are lightly charred, 3 to 5 minutes. Transfer to a plate and chop when cool enough to handle.

Add the shrimp to the pan and cook, turning once, until just opaque, 2 to 3 minutes.

Divide the rice between two dinner bowls. Top each with equal portions of shrimp, charred lettuce, cucumber, and carrot. Pour over the reserved sauce, sprinkle with some peanuts and cilantro, garnish with a lime wedge, and serve.