In a large pot or Dutch oven, heat the olive oil and butter over medium heat until butter melts and foams. Add the diced onion, carrot, and celery. Cook, stirring occasionally, until the vegetables are softened and the onion is translucent, about 6–8 minutes. Add the minced garlic and cook another 30–60 seconds until fragrant.

Proteins & Vegetables

Add heartier vegetables

Add the diced potato and sliced mushrooms to the pot. Cook, stirring, for 3–4 minutes to start softening and to build flavor.

Add remaining vegetables and tomato

Stir in the zucchini and the canned diced tomatoes with their juices, distributing them evenly.

Liquids & Seasoning

Add stock and seasonings

Pour in the chicken or vegetable stock and the cup of water. Add the bay leaf, dried thyme, dried oregano, salt, black pepper, and red pepper flakes. Stir to combine and bring the mixture to a gentle boil over medium-high heat.

Simmer

Once boiling, reduce heat to low and simmer, partially covered, until the potatoes are tender and flavors have melded, about 20–25 minutes. Taste and adjust seasoning if needed; remove the bay leaf.

Add cooked protein

If using cooked shredded chicken, stir it in during the last 5 minutes just to heat through. For a vegetarian version, omit the chicken.

Finishing

Finish and serve

Remove the pot from heat. Stir in the chopped parsley and lemon juice. Ladle soup into bowls and top each serving with a sprinkle of grated Parmesan if desired. Serve hot.