Heat a large cast-iron saucepan (cauldron) over medium-high heat, pour olive oil, heat.
Pour onions, carrots, celery and garlic into a saucepan, fry, stirring occasionally, for about 5 minutes.
Add broth, water, tomatoes, basil, black pepper and bay leaf into the cauldron, bring to a boil over high heat. Reduce heat and cook vegetables for about 2 minutes.
Place the tortellini and bok choy in a saucepan, cook for about 7 minutes until the pasta is done. Remove bay leaves and serve soup immediately.