01 - Rinse barley under cold water. In a medium saucepan, bring 3 cups water and 1/2 teaspoon salt to a boil. Add barley, reduce heat to a simmer, cover, and cook for 25-30 minutes until tender. Drain excess water and let cool slightly.
02 - Segment the orange and grapefruit, removing all membranes and seeds. Place segments in a bowl and reserve any released juices for the dressing.
03 - In a small bowl, whisk together lemon juice, lemon zest, olive oil, honey or maple syrup, Dijon mustard, black pepper, and sea salt. Add any reserved citrus juice from the segmented fruit.
04 - In a large bowl, combine cooled barley, arugula, red onion, and cucumber. Drizzle with the prepared dressing and toss gently to coat evenly.
05 - Gently fold the citrus segments into the dressed mixture. Top with toasted sliced almonds and crumbled feta cheese if desired.
06 - Serve immediately at room temperature, or refrigerate for up to 2 hours to allow flavors to meld together.