Roast the Beets: Preheat oven to 400°F (200°C). Peel and dice beets into ¾-inch cubes. Toss with olive oil, salt, pepper, and rosemary.
Spread on a parchment-lined pan and roast for 30–40 minutes, turning halfway until tender and caramelized.
Cook the Quinoa: Rinse quinoa under cold water. In a saucepan, bring water or broth to a boil. Add quinoa and salt, reduce heat, cover, and simmer for 15 minutes or until fluffy. Let it rest for 5 minutes, then fluff with a fork.
Toast the Walnuts: In a dry skillet over medium heat, toast walnuts for 3–4 minutes until fragrant. Stir often to avoid burning.
Make the Dressing: Whisk olive oil, balsamic vinegar, honey, Dijon, salt, and pepper until smooth.
Assemble the Bowls: Arrange arugula and quinoa on plates. Top with roasted beets, walnuts, and crumbled feta. Drizzle with dressing and add orange slices or zest for brightness.