Sauté onions in olive oil until tender. Add tomato, celery and artichoke hearts; sauté for 5 more minutes. Add water, lentils, bulgur, garlic, salt and pepper. Bring to a boil; let boil for 5 minutes then turn heat down to simmer for 25 more minutes. Stir occasionally. Remove from heat and let stand 15 minutes. Drain excess water; refrigerate.