Prepare the pastry - Take the puff pastry sheet out of the fridge and let it sit at room temperature for 10-15 minutes until thawed but still cold to the touch. Dust a clean work surface with flour and gently unfold the pastry sheet. Using a sharp knife, cut the sheet in half lengthwise to create two long rectangles.

Prepare the sausage filling - Preheat the oven to 375°F (190°C). In a large skillet over medium heat, add a tablespoon of olive oil and chopped onions and garlic, and sauté until the onions are soft and the garlic is fragrant, about 5-7 minutes. Remove from heat and cool slightly. Add the hoisin sauce to the onion mixture, stirring to combine well. Cut the vegan sausages in half lengthwise, then cut in half again crosswise, to get 4 short sausage pieces from one sausage. Add the sausage pieces to the onion mixture, and toss to coat well.

Assemble the rolls - Arrange one of the pastry rectangles lengthwise in front of you. Brush the bottom half of the pastry lightly with water. Arrange 6 sausage pieces in a single line along the bottom half of the pastry rectangle, leaving a slight gap between them. Roll the pastry over the sausage, gently pressing the edges to seal. Cut the sausage roll into 6 equal pieces using a sharp knife. Transfer the rolls to a baking sheet lined with parchment paper and lightly pierce the top of each roll with a fork or pastry docker to allow steam to escape. Repeat with the second pastry rectangle and the remaining sausage pieces.

Bake the rolls - Bake the rolls for 20-25 minutes or until golden and puffed. Remove from the oven and let cool for a few minutes before serving.