Peel cucumber, either leaving strips of green (if the cucumber has thin skin) or peeling all the skin (if the cucumber has thick waxy skin).: The first thing you will notice is the fresh, green aroma as the cucumber skin comes away, and leaving alternating strips of skin gives a pretty striped look and a hint of bitterness that some people love. If you choose to peel all the skin, the surface will feel smoother and the bites will be milder in flavor. One common mistake is using a cucumber that is overripe and soft, which yields a soggy base; always pick a firm specimen.
Slice cucumber into thick slices about 3/4 – 1 inch thick. If the cucumbers seem watery, use a paper towel to press down on both sides to absorb some of the water and dry the surface of the cucumber.: You should hear a crisp, clean sound as the knife cuts through the flesh, and the cut faces should look glossy and moist but not dripping. Drying the rounds briefly with a paper towel helps the hummus adhere, and pressing gently will release excess surface water without crushing the structure. Avoid slicing them too thin, which makes them flop under the topping, or too thick, which can overwhelm the balance of bite to topping.
Put hummus into a small bag made of thick plastic. I used 1/2 cup hummus to make 14 appetizers; you can always add more hummus to the bag if you prefer a thicker mound of hummus.: When you spoon the hummus into a bag the texture becomes more controllable, and you will notice the cool, creamy smell of chickpeas and tahini as you work. The bag method creates neat mounds quickly, which is especially helpful when serving a group. A common slip is cutting too large a bag tip, which leads to puddles rather than neat swirls, so cut a small opening first and enlarge if needed.
Cut off one corner of the bag so you can squeeze the hummus out, taking care not to make the hole too big.: A small opening produces a clean, dense dollop, while a large hole leads to a flat smear. As you squeeze, watch for smooth, even piping and listen for the gentle squish as the hummus moves through the bag. If the texture is too thick to squeeze easily, soften it slightly with a teaspoon of water and mix, but be careful not to make it runny. The typical error here is impatience, which results in uneven mounds; steady, even pressure creates the best shape.
Arrange cucumber slices on a plate or serving tray, then squeeze a mound of hummus on to the top of each cucumber slice.: The visual impact is important, so arrange the rounds in a tidy grid or in concentric circles for effect. As you deposit the hummus , notice the contrast between the pale cream and the green cucumber; that contrast is part of the appeal. If a mound feels unstable, press it gently into the cucumber so it adheres without flattening. A frequent misstep is overcrowding the tray, which leads to messy handling when guests reach for them, so leave some space between pieces.
Sprinkle slices with sesame seeds just before serving.: The final flourish should be light and deliberate, adding a whisper of toasty aroma and tiny crunchy pops. Sprinkling just before serving helps the seeds stay crisp and keeps the presentation fresh. If you do this too early, the seeds can settle into the hummus and lose their texture. One simple troubleshooting note is that using a spoon to scatter seeds often produces uneven coverage, so I prefer pinching a small handful and gently scattering for a more controlled finish.