01 - Preheat the oven to 425°F. Line a baking sheet with parchment paper.
02 - Toss sliced zucchini, red onion, and cherry tomatoes with 2 tablespoons olive oil, oregano, salt, pepper, and optional red pepper flakes. Spread in a single layer on the prepared baking sheet.
03 - Roast vegetables for 18-22 minutes, stirring halfway through, until golden and tender.
04 - While vegetables roast, rinse quinoa under cold water. In a saucepan, heat 1 tablespoon olive oil over medium heat. Add quinoa and toast for 1-2 minutes, stirring constantly.
05 - Add 2 cups water or vegetable broth, bring to a boil, then reduce heat, cover, and simmer for 15 minutes or until liquid is absorbed. Remove from heat and let stand, covered, for 5 minutes. Fluff with a fork.
06 - In a bowl, mix yogurt, lemon zest, lemon juice, olive oil, minced garlic, salt, and black pepper until smooth and well combined.
07 - Divide quinoa among 4 bowls. Top with roasted vegetables and fresh spinach or arugula. Drizzle with lemon yogurt and sprinkle with chopped pistachios.
08 - Serve immediately, or chill for 30 minutes for a cold grain bowl option.