Toss squash with 1 Tbsp oil, a ½ tsp garlic powder, and a ¼ tsp salt. In a separate bowl, toss broccoli, cauliflower, and onion with 1 Tbsp oil, ½ tsp garlic powder, and ¼ tsp salt.
Spread squash across a rimmed baking sheet. Bake at 425 for 8 minutes. Remove from oven and stir. Add broccoli mixture to squash on baking sheet, evenly spreading vegetables across baking sheet. Bake for 8 to 10 minutes, or until squash is tender and vegetables are beginning to brown.
In a small bowl, whisk together oil, vinegar, syrup, mustard, and a dash of salt and pepper, if desired.
To assemble bowls, divide greens evenly among 4 bowls. Top each evenly with warm quinoa, followed by roasted vegetables. Drizzle with dressing.