Heat a large heavy-bottomed pot or Dutch oven over medium heat. Add 2 tablespoons olive oil. When shimmering, add the diced onion, carrots, and celery. Cook, stirring occasionally, until the vegetables have softened and the onion is translucent, about 6–8 minutes.

Add garlic and root vegetables

Add the minced garlic and cook for 30–45 seconds until fragrant. Add the diced potato and zucchini, stir to combine, and cook for 2–3 minutes to begin softening.

Add tomatoes, broth and seasonings

Pour in the canned diced tomatoes (with juices) and the 6 cups of broth. Add the dried thyme, dried oregano, bay leaf, 1 1/2 teaspoons kosher salt, and 1/2 teaspoon freshly ground black pepper. Stir, increase heat to bring the pot to a gentle boil, then reduce heat to maintain a simmer.

Simmer until tender

Cover partially and simmer for 20–25 minutes, until the potatoes and carrots are tender when pierced with a fork.

Finish with greens and brightening

Remove and discard the bay leaf. Stir in the chopped spinach and cook 2–3 minutes until wilted. Add the chopped parsley and 1 tablespoon fresh lemon juice. Taste and adjust seasoning with additional salt, pepper, or lemon juice as desired.

Serve

Ladle soup into bowls and top with grated Parmesan and a pinch of red pepper flakes if using. Serve with crusty bread on the side.

Optional Garnish / Add-ins

To add protein: stir in 1–2 cups cooked shredded rotisserie chicken or canned beans (drained and rinsed) during the last 5 minutes of simmering to heat through. For a creamier texture, puree one cup of the cooked soup and stir back in.

To make ahead and store: cool soup to room temperature, refrigerate in an airtight container up to 4 days or freeze up to 3 months. Reheat gently on the stove, adding a splash of broth if thicker after chilling.