Heat the annatto oil in a pan over medium heat. Add the minced shallots and sauté until fragrant. Add the pork and stir-fry until it firms up. Add 1 teaspoon seasoning powder, 1 teaspoon sugar, and 1 teaspoon fish sauce. Once the pork is cooked, add the shrimp and stir until both are cooked through. Add the black pepper, mix well, then remove from heat.

Dip each rice paper wrapper in water to soften, then lay it flat on a clean plate. Place a spoonful of the pork and shrimp filling in the center, fold the edges, and roll up tightly to resemble bánh bột lọc wrapped in banana leaves. Repeat until all 40 wrappers are used. (Lightly brush the plate with vegetable oil before placing the rolls on it.)

Bring water to a boil in a steamer. Steam the rolls for 8 minutes.

For the dipping sauce:
- Mix 3 tablespoons sugar, 3 tablespoons fish sauce, and 2 tablespoons water in a bowl until the sugar dissolves. Add sliced chili pepper.
For the scallion oil:
- Heat 4 tablespoons vegetable oil until hot, then pour over the chopped green onions in a bowl.

Once the rolls are cooked, remove them from the steamer, top with scallion oil, and serve with the dipping sauce.