Preheat your oven to 400°F (200°C). Spread the pumpkin cubes and Brussels sprouts on a baking sheet, ensuring they are in a single layer. Drizzle with olive oil and sprinkle with salt and pepper. Cook quinoa according to the package.
Roast in the oven for 20-25 minutes or until the vegetables are tender and slightly caramelized. Give them a good toss midway through the cooking time.
Add a generous drizzle of olive oil in a skillet over medium heat. Add the thinly sliced onions, stirring occasionally, and let them cook slowly until they turn a deep, golden brown color.
In a dry skillet over medium heat, toast the walnuts, stirring occasionally until they are lightly browned and aromatic. This should take about 3-5 minutes. Set them aside to cool.
Whisk the olive oil, balsamic vinegar, honey or maple syrup, minced garlic, salt, and pepper in a small bowl. Taste and adjust seasoning if necessary.
Mix the roasted pumpkin, Brussels sprouts, caramelized onions, and cooked quinoa in a large serving bowl. Drizzle over the dressing and toss until everything is well coated.
Top with the toasted walnuts and pomegranate seeds. Serve the salad either warm or at room temperature.