01 - Preheat oven to 400°F. Line a baking sheet with parchment paper.
02 - Toss carrot sticks and red onion slices with 1 tbsp olive oil, salt, and pepper. Spread on the prepared baking sheet. Roast for 25-30 minutes, turning halfway, until tender and lightly caramelized.
03 - Rinse barley thoroughly. In a medium saucepan, combine barley, water, and 1/2 tsp salt. Bring to a boil, reduce heat, cover, and simmer for 25-30 minutes or until barley is tender. Drain excess water if needed.
04 - In a small bowl, whisk together remaining olive oil, lemon juice, Dijon mustard, honey, garlic, salt, and pepper to make the dressing.
05 - In a large bowl, combine warm barley, roasted carrots and onions, and baby spinach. Drizzle with dressing and toss gently until well mixed and spinach is slightly wilted.
06 - Transfer to a serving platter. Top with crumbled feta, toasted walnuts, and fresh parsley. Serve warm or at room temperature.