Preheat the oven to 400°F (200°C).
Rinse the quinoa under cold water and drain. In a pot, combine the rinsed quinoa and 2 cups of water or vegetable broth. Bring to a boil, reduce heat to low, cover, and simmer for 15 minutes or until the quinoa is fluffy and liquid is absorbed. Remove from heat and let it sit covered for 5 minutes.
On a baking sheet, toss the diced zucchini, red bell pepper, cherry tomatoes, and sliced red onion with olive oil, salt, pepper, dried oregano, and garlic powder.
Roast the vegetables in the preheated oven for about 25 minutes, or until they're tender and slightly charred. Stir halfway through cooking for even roasting.
In a mixing bowl, whisk together tahini, lemon juice, maple syrup (if using), and 1-2 tablespoons of water until smooth and creamy to prepare the dressing.
Once the quinoa is cooked, fluff it with a fork and divide it among four bowls. Top with the roasted vegetables and drizzle with the lemon-tahini dressing.
Garnish with fresh parsley or cilantro if desired. Serve warm or at room temperature.