To assemble each of the four crab stacks, begin by placing a layer of diced avocado in the mold, pressing it down firmly, and then topping it with a layer of crab. Next, pack a layer of tomatoes on top of the crab, followed by diced mango. Arrange a layer of sliced cucumbers on top of the mango, fanning them out to fill the circular mold. Then, add diced red onions as the next layer, followed by microgreens.