Heat the olive oil in a large pot or Dutch oven over medium heat. Add the onion, carrots and celery and cook for 5–6 minutes, until the onion is soft.
Stir in the garlic and Italian seasoning and cook for 30 seconds.
Add the potatoes, diced tomatoes with their juices, broth, bay leaf, salt and pepper. Bring to a boil.
Reduce the heat and simmer, partly covered, for 15–20 minutes, until the potatoes are tender.
Stir in the frozen vegetables and simmer for 5 minutes more.
Remove the bay leaf and stir in the lemon juice. Taste and add more salt and pepper if needed, then serve.