Heat olive oil in a large Dutch oven over medium heat. Add the onion and the next 7 ingredients (onion through bay leaf); cook 10 minutes. Add the water and lentils, and bring to a boil. Reduce heat, and simmer 30 minutes. Add spinach, bulgur, barley, and chickpeas; cook 1 minute. Remove from heat, and discard bay leaf. Cover mixture and let stand 15 minutes.
Spoon the yogurt onto several layers of heavy-duty paper towels, spreading to 1/2-inch thickness. Cover yogurt with additional paper towels, and let stand 5 minutes. Scrape yogurt into a bowl using a rubber spatula. Serve the drained yogurt with potage.