1. Peel and shred the carrots, using a julienne peeler or box grater. Slice the tops off of the broccoli and the cauliflower into very small pieces. Thinly slice the green onions.
2. Spread about 2 tablespoons of hummus onto a tortilla in a thin layer. Sprinkle another thin layer vegetables on top, taking care not to overfill and leaving the very top of the tortilla without vegetables. Starting from the bottom of the circle, tightly roll the tortilla; as you roll to the top, the vegetables will naturally move up and distribute evenly through the rollup. Use a serrated knife to cut the roll into 6 or 8 pieces. If desired, spear with toothpicks. Refrigerate until serving.