In a mortar, pound the garlic to a paste with the brown sugar and green curry paste. Add the lime juice, fish sauce and 3 tablespoons of water. Stir in half of the cilantro and mint. In a small bowl, whisk the mayonnaise with 1 tablespoon of the green curry dipping sauce.
In a large bowl, toss the coleslaw mix with the roast beef and the remaining cilantro and mint.
Fill a pie plate with warm water. Dip 2 or 3 rice paper wrappers at a time in the water, then set them on a work surface to soften, about 1 minute. Spread a scant teaspoon of the curry mayonnaise on the bottom third of each wrapper and top with a scant 3 tablespoons of the roast beef filling. Roll the wrappers into tight cylinders, tucking in the sides as you go. Transfer the rolls to a plastic wrap–lined baking sheet and repeat with the remaining wrappers, curry mayonnaise and filling.
Just before serving, cut each roll in half and serve with the dipping sauce.