Prep and Season: Preheat your oven to 400°F. Toss the diced sweet potato and Brussels sprouts in a large bowl with 1 tablespoon olive oil, 1 teaspoon salt, and 1 teaspoon freshly ground black pepper until evenly coated.
Spread and Roast: Spread the vegetables in a single layer on a large baking sheet. Roast for 25 to 30 minutes, stirring halfway through, until the sweet potatoes are tender and the Brussels sprouts are caramelized and golden brown.
Sauté the Onion: In a medium saucepan, heat 2 tablespoons olive oil over medium heat. Add the diced red onion and cook for 3 to 4 minutes, stirring occasionally, until softened and slightly translucent.
Toast and Cook Quinoa: Add the dry quinoa to the pan and toast for 2 to 3 minutes, stirring frequently, until fragrant and lightly golden. Pour in 1½ cups water and bring to a boil, then reduce heat to low, cover, and simmer for 15 minutes until the water is absorbed and the quinoa is tender.
Fluff and Cool: Remove from heat and let stand for 5 minutes covered, then fluff with a fork and transfer to a large mixing bowl to cool slightly.
Combine Base: To the cooled quinoa, add the roasted sweet potato and Brussels sprouts, fresh spinach, drained chickpeas, and dried cranberries. Toss gently to combine.
Make the Dressing: In a small bowl, whisk together 2 tablespoons lemon juice, 1 tablespoon apple cider vinegar, 1 tablespoon maple syrup, 1 tablespoon olive oil (if using), 1 teaspoon garlic powder, and 1 tablespoon fresh parsley. Taste and adjust seasonings as needed.
Dress and Top: Pour the dressing over the salad and toss until all ingredients are well coated. Top with 6 ounces crumbled feta cheese and serve immediately, or refrigerate for up to 4 days.