01 - Set oven temperature to 425°F. Line a baking sheet with parchment paper.
02 - Toss diced zucchini and red bell pepper with 1 tablespoon olive oil, a pinch of sea salt, and black pepper. Distribute mixture evenly across the prepared baking sheet.
03 - Place vegetables in oven and roast for 20 to 25 minutes, stirring midway, until tender and golden. Set aside for later use.
04 - In a medium saucepan, combine rinsed quinoa and water or vegetable broth. Bring to a boil over medium-high heat, reduce to low, cover, and simmer for 15 minutes or until liquid is absorbed. Remove from heat and allow to stand, covered, for 5 minutes. Fluff quinoa with a fork.
05 - In a small bowl, whisk remaining olive oil with lemon juice, Dijon mustard, minced garlic, sea salt, and black pepper until fully emulsified.
06 - Transfer cooked quinoa, roasted zucchini and bell pepper, cherry tomatoes, and red onion into a large mixing bowl. Drizzle with the prepared dressing and gently toss to coat evenly.
07 - Fold in chopped parsley, chopped mint, and crumbled feta cheese if desired. Serve warm or at room temperature.