Heat oil in a heavy stockpot; add the onion and garlic and sauté for several minutes or until the onion is limp and translucent.

Add broth and lentils and bring to a boil; reduce heat, cover pot, and simmer for about 30 minutes.

Next, add carrots, potatoes, Swiss chard, and bay leaves.

Bring to a boil again, and then reduce heat and simmer until the lentils and vegetables are tender, about 20 minutes.

Next, add the cooked ham, tomatoes, basil, thyme, and pepper; simmer for 10 minutes more.

Discard bay leaves.

Ladle stew into individual bowls, sprinkle with parsley if using, and serve.