This thick soup can be made ahead of time and refrigerated for several days before serving. You can also freeze it for up to 3 months.
Heat oil in a large pan over medium heat. Add onions and cook for 2 minutes, or until they begin to soften. Add garlic and salt and continue cooking for 1 minute. Do not let onions or garlic brown. If they start to brown, turn down the heat.
Add carrots, celery, lentils and barley to pot. Stir to coat with onions. Add crushed tomatoes, vegetable stock and water. Stir to combine ingredients.
Stir in remaining ingredients (pepper, sugar, oregano, basil, thyme, sage and pepper flakes) and bring soup to a boil over medium high heat. Reduce heat to medium-low or low to maintain a simmer, and cover. Simmer for 40-45 minutes, stirring occasionally to keep soup from sticking.
Serve soup hot, or refrigerate or freeze until needed.