Heat olive oil in a heavy pot over medium heat. Add onion, garlic, and celery; sauté until translucent and lightly caramelized, 8–10 minutes, stirring often.
Stir in diced carrots, pour in broth, and add thyme and bay leaf. Bring to a gentle boil, then reduce to a low simmer. Cover and cook 25–30 minutes until vegetables are tender.
Remove bay leaf. Stir in cooked barley or rice. If using uncooked grains, simmer longer until tender (barley 20–30 min, rice 15–20 min). Adjust salt and pepper; add a squeeze of lemon if desired.
Serve hot. Optional garnishes: fresh herbs, swirl of olive oil, or a spoon of Greek yogurt.
