Combine hoisin sauce, coconut milk, rice vinegar, and onion in a blender and puree until smooth for the dipping sauce.

Transfer the sauce to a saucepan and bring to a boil over medium heat.

Reduce heat and simmer for 5 minutes, adding water to adjust consistency as needed.

Let the sauce cool completely.

Julienne the cooked pork loin into thin strips.

Chop the cooked shrimp into 1/2-inch pieces.

Boil rice vermicelli for 2-3 minutes.

Rinse the cooked vermicelli in cold water and drain thoroughly.

Separate cilantro into sprigs of the appropriate size for the rolls.

Briefly wet each rice paper sheet, one at a time, and blot on paper toweling.

On each rice paper, place some noodles, pork, shrimp, lettuce, bean sprouts, basil, and cilantro.

Fold in the sides of the rice paper.

Wrap the top down and roll up tightly, envelope style.

Place each completed roll on a plate and cover with a damp paper towel to prevent drying.

Pour the dipping sauce into small bowls and garnish with chopped roasted peanuts.

Serve the goi cuon immediately with the dipping sauce and hot chili sauce, if desired.