Wash and dry all vegetables. Finely chop the onion to measure 1 cup. Peel and dice carrots and potato into roughly 1/2-inch pieces so they cook evenly. Dice the celery and zucchini. Mince the garlic. Roughly chop the spinach or kale and chop parsley for garnish.

Sweat aromatic vegetables

Heat a large heavy-bottomed pot over medium heat. Add 2 tablespoons olive oil and swirl to coat. When the oil shimmers, add the chopped onion, carrot, and celery. Cook, stirring occasionally, until the onion is translucent and the vegetables begin to soften, about 6–8 minutes. Add the minced garlic and cook 30–45 seconds more until fragrant, taking care not to brown it.

Add potatoes, tomatoes and seasonings

Stir in the diced potato and zucchini, then add the entire 14.5 oz can of diced tomatoes with their juices. Sprinkle in the dried thyme (1 tsp), dried oregano (1 tsp), bay leaf, salt (1 tsp) and black pepper (1 tsp). Stir to combine and cook for 1–2 minutes to marry flavors.

Simmer with broth

Pour in 6 cups of low-sodium vegetable broth, scraping any browned bits from the bottom of the pot. Increase heat to bring the mixture to a gentle boil, then reduce heat to maintain a simmer. Cover partly and simmer until the potatoes and carrots are tender when pierced with a fork, about 18–22 minutes.

Finish with greens and optional add-ins

Remove and discard the bay leaf. Stir in 2 cups chopped spinach or kale and, if using, 1 cup cooked beans and/or 1 cup cooked pasta or rice. Simmer uncovered for 3–4 minutes until the greens are wilted and any add-ins are heated through.

Adjust seasoning and brighten

Taste the soup and adjust salt and pepper as needed. If desired, stir in 1 tablespoon fresh lemon juice to brighten flavors. If you prefer a thicker texture, use an immersion blender to purée 1 to 2 cups of the soup and stir back in.

Serve

Ladle the soup into bowls, garnish with 2 tablespoons chopped fresh parsley and a sprinkle of grated Parmesan if using. Serve with crusty bread or croutons. Leftovers keep covered in the fridge for up to 4 days and freeze well for up to 3 months.