Start by rinsing the quinoa thoroughly under cold water using a fine mesh strainer. This removes the natural coating that can taste bitter. In a saucepan, combine quinoa with water or broth and bring it to a boil, then reduce to a gentle simmer and cover. Cook for about 15 minutes until the liquid is absorbed and the grains are tender, then fluff with a fork and let it cool slightly.
Preheat your oven to 425°F (220°C) while you chop the vegetables into evenly sized pieces. Toss zucchini, squash, bell pepper, onion, and tomatoes with olive oil, salt, and pepper until well coated. Spread them in a single layer on a baking sheet and roast for 20–25 minutes, stirring halfway through, until tender and lightly caramelized around the edges.
In a small bowl, whisk together lemon juice, lemon zest, red wine vinegar, and a drizzle of olive oil if desired. The dressing should taste bright and balanced, not overly acidic. Adjust salt and pepper to taste, remembering that feta will add extra saltiness later.
In a large mixing bowl, add the cooked quinoa and roasted vegetables while they are still slightly warm. Pour the dressing over the mixture and toss gently so everything is evenly coated. Sprinkle chopped parsley and feta on top, folding carefully to maintain texture.
You can serve the salad warm, at room temperature, or chilled depending on your preference. I like letting it sit for at least 20 minutes before serving so the flavors meld together beautifully. Give it one final toss and adjust seasoning before plating.