Rinse the barley under cold water.
Bring water and salt to a boil. Add barley.
Lower heat and simmer uncovered for 25–30 minutes until tender but chewy.
Drain well and spread on a tray to cool slightly.
Heat oven to 425°F (220°C).
Toss mushrooms, bell pepper, zucchini, and red onion with olive oil, pepper, and smoked paprika.
Spread vegetables on a baking sheet in a single layer.
Roast for 20–25 minutes, flipping once, until browned and soft.
In a small bowl, whisk lemon juice, lemon zest, olive oil, Dijon mustard, and garlic.
In a large bowl, add warm barley and roasted vegetables.
Pour dressing over the mixture and gently toss.
Add parsley and mint. Mix lightly.
Top with feta if using. Taste and adjust salt if needed.
Serve warm or cold.
