I used dried lentils, but you could certainly used canned. If you do choose to use the latter, make sure to rinse them well, and add them about 10 minutes before serving instead of letting them boil with the rest of the soup.
1 large sweet potato, peeled & diced (about 1 cm pieces)
1 cup dry red lentils (or 2 cups canned)
1 onion, chopped
2 cloves garlic, minced
2 cups diced tomatoes
4 cups reduced-sodium vegetable broth
1 tsp oregano
1 bay leaf
1. Heat oil in large saucepan. Add onion & garlic and cook until translucent.
2. Add sweet potatoes and lightly brown, about 3 minutes.
3. Add remaining ingredients. Bring to a boil, reduce heat and simmer for 45 minutes.
4. Remove bay leaf.
5. Serves 6