Heat the olive oil in a large Dutch oven over medium heat.

Add the diced pancetta or smoked kielbasa and cook until browned and slightly crisp, about 5 minutes.

Add the chopped onion, carrots, and celery. Sauté until onions are translucent, about 6 minutes.

Stir in the minced garlic and cook for 1 minute more until fragrant.

Stir in oregano, thyme, red pepper flakes (if using), and tomato paste. Cook for 1-2 minutes.

Pour in the diced tomatoes with their juices and scrape any browned bits off the bottom of the pot. Let the mixture simmer for 2-3 minutes.

Add the chicken broth, drained cannellini beans, and bay leaf. Bring to a gentle boil, then reduce heat to low.

Simmer the soup uncovered for 20-25 minutes to let flavors combine and vegetables soften.

Remove the bay leaf. For a creamier texture, purée 1 to 2 cups of the soup using an immersion blender.

Stir in lemon juice or vinegar and season with salt and pepper to taste.

Ladle into bowls and garnish with chopped fresh parsley or basil.