Combine ground pork, minced garlic, sugar, fish sauce, oyster sauce, cornstarch, black pepper, and 1 tbsp oil in a large bowl. Mix thoroughly until the mixture becomes sticky and well combined. Wet your hands with water and shape the mixture into 8 sausage-shaped logs.

Preheat a grill pan or outdoor grill over medium-high heat. Grill the pork sausages for 10-12 minutes, turning occasionally, until golden brown and cooked through. Set aside to rest.

Mix fish sauce, lime juice, sugar, and water in a small bowl until completely dissolved. Stir in minced garlic and sliced chili. Taste and adjust sweetness or acidity as desired.

Rinse and thoroughly dry lettuce, mint, and cilantro. Julienne the cucumber and carrot into thin, uniform strips.

Fill a large shallow dish with warm water. Dip a rice paper wrapper into the water for 5-7 seconds until just pliable. Lay the softened wrapper on a clean, damp kitchen towel.

Place a lettuce leaf on the lower third of the wrapper. Top with a small bundle of vermicelli, some cucumber, carrot, and a few mint and cilantro leaves. Add one grilled pork sausage. Fold the sides inward and roll up tightly from the bottom to enclose the filling completely.

Repeat with remaining ingredients to make 8 rolls. Serve immediately with the prepared dipping sauce for the best texture and flavor.