Prepare the cucumber by using a vegetable peeler to peel full-length slices from a whole piece. For reference, 1 ounce of cucumber will be about 10 slices. Arrange the slices in single layers between paper towels, and press down on the paper towels to absorb excess water. When the cucumber slices no longer feel wet, weigh the slices to yield the amount listed in the ingredients. You may discard any remaining cucumber slices or use them for another recipe.
Lay a sheet of roasted seaweed (also called nori) on a clean, dry surface. Arrange the cucumber slices across the sheet of nori in a single layer. If necessary, you can cut the cucumber slices in half so you can arrange all the cucumber to fit within the sheet of nori. In a separate mixing bowl, combine lump crab and Sriracha. Mix the ingredients until the crab is coated in Sriracha. At your discretion, you may season the crab to your liking. Remember, however, that sushi is meant to be fresh and simple.
Arrange the seasoned lump crab in a strip across the edge of nori nearest you. You can gently pack the crab down so it’s easier to roll the sushi later. Slice fresh avocado into thin slices and arrange them in a row alongside the crab. Next, cut cold cream cheese into thin strips and line up the strips end-to-end across the crab. If your cream cheese is warm, you won’t be able to have the clean cuts that are needed.
Begin rolling the sushi up, starting at the end with all the filling. You may use a knife or other utensil to help you lift the edge of the nori up and fold over the filling to begin the roll. You can use your hands or a sushi-making tool to roll the sushi up into a tight roll, rolling the seam underneath at the end. Make sure your hands are clean and dry or else the delicate nori may tear. Use a super-sharp knife to cut each sushi roll into 6 pieces.