Heat the oil in a stockpot pot or Dutch oven over medium heat. Add the onions, carrots, celery, and tomato paste. Cook, stirring often until the vegetables have softened and the onions are translucent; 8 to 10 minutes.
Add the garlic, fennel, black pepper, ½ teaspoon of salt, and the red pepper flakes. Cook, while stirring, for one minute.
Pour in the tomatoes and their juices as well as the stock/broth.
Add the potatoes, cabbage, and bay leaves. Raise the heat to medium-high and bring the soup to a boil. Partially cover the pot with a lid, and then reduce the heat to maintain a low simmer.
Simmer for 20 minutes or until the potatoes, and other vegetables are tender. Add the frozen peas and cook for five more minutes.
Remove the pot from the heat and remove the bay leaves. Stir in the lemon juice. Taste and season with more salt, pepper or vinegar. Serve.