Preheat the oven to 425°F (220°C).
Cook the quinoa: combine the rinsed quinoa and vegetable stock in a small saucepan and bring to a boil, then reduce heat and simmer until liquid is absorbed and the quinoa tails pop, about 15 minutes; remove from heat and let cool.
Prepare the Brussels sprouts: place halved sprouts on a baking sheet, drizzle with 1 tablespoon olive oil, season with onion powder, garlic powder, salt, and pepper, and toss to coat; arrange cut side down in a single layer.
Roast the Brussels sprouts until golden and tender, about 20 minutes; remove and set aside to cool slightly.
Make the dressing: in a blender combine soaked and drained cashews, 3 garlic cloves, nutritional yeast, capers, lemon juice, 1 tablespoon olive oil, Dijon mustard, vegan Worcestershire, hot sauce, 1/3 cup water, and salt and pepper; blend on high until very smooth and creamy, about 1 minute, then taste and adjust seasoning.
Assemble the salad: in a large wide bowl combine the cooked quinoa, roasted Brussels sprouts, and rinsed lentils and toss gently to combine.
Drizzle the spicy Caesar dressing over the salad, then top with pickled red onions, chopped sun-dried tomatoes, toasted sunflower seeds, and chopped parsley or chives if using; finish with freshly cracked black pepper and serve.