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; reduce heat, cover, and simmer until the liquid is absorbed and the quinoa tails have popped, about 15 minutes. Remove from heat and let cool.
Toss the halved Brussels sprouts with 1 tablespoon olive oil, onion powder, garlic powder, salt, and pepper in a bowl or on the baking sheet so they are evenly coated.
Arrange the Brussels sprouts cut-side down in a single layer on a baking sheet and roast until golden and tender, about 20 minutes. Remove and set aside.
Make the spicy Caesar 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 sauce, hot sauce, 1/3 cup water, and salt and pepper to taste. Blend on high until completely smooth and creamy, about 1 minute; adjust seasoning as needed.
Assemble the salad: in a large wide bowl combine the cooked quinoa, roasted Brussels sprouts, and cooked lentils; 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.
