Step 1. Transfer the Brussels sprouts and sweet potatoes to a large rimmed baking sheet in a single layer. Toss with olive oil, onion and garlic powders, and salt.
Step 3. Transfer the cooked lentils to a medium baking sheet in a single layer. Toss with olive oil, onion and garlic powders, and salt. Place in the oven on the top rack. Roast for about 15 minutes, or until crispy.
Step 4. Transfer the tahini, cumin, salt, and lemon juice to a medium bowl. Grate or press the garlic into the bowl. Add the ice-cold water 1 tablespoon at a time until the desired consistency.