Peel and cut the carrots into 1/2-inch rounds. Cube the potatoes into 1-inch pieces. Slice the celery, dice the onion and red bell pepper, halve or quarter mushrooms, trim and halve the green beans, and cut zucchini into 1/2-inch half-moons. Mince the garlic and chop the parsley. Reserve thyme sprigs.

Measure out the vegetable stock, diced tomatoes (with juices), and tomato paste so they are ready when assembling the pot or slow cooker.

Searing (optional but recommended)

Lightly brown vegetables

In a large skillet over medium heat, add 1 tablespoon of olive oil. Add onions and a pinch of salt and cook 3–4 minutes until translucent. Add carrots and celery and cook 4–5 minutes until they begin to color. Transfer this mixture to the slow cooker or a large heavy-bottomed pot. If using mushrooms, brown them in the same skillet 3–4 minutes before adding.

Slow cooking

Combine and cook

Place the remaining vegetables (potatoes, zucchini, red pepper, green beans, and any browned mushrooms) into the slow cooker or pot with the onion-carrot-celery mixture. Add the diced tomatoes with their juices, tomato paste, minced garlic, thyme sprigs, bay leaf, dried oregano, smoked paprika, salt, and pepper. Pour in the vegetable stock and stir to combine. Drizzle the remaining 1 tablespoon of olive oil over the top.

Cook time

If using a slow cooker: cover and cook on LOW for 6–7 hours or HIGH for 3–4 hours, until vegetables are tender but not disintegrating. If using the stove/oven: bring to a gentle simmer over medium-low heat, cover and simmer on the stovetop for 30–40 minutes until vegetables are tender, or bake covered at 350°F (175°C) for 30–40 minutes.

About 15 minutes before the end of cooking, remove the thyme sprigs and bay leaf. Taste and adjust seasoning with additional salt and pepper if needed.

Finish & serve

Stir in the chopped parsley and lemon juice (if using) to brighten the flavors. If you prefer a slightly thicker broth, mash 1/2 cup of the potatoes against the side of the pot and stir, or simmer uncovered for 5–10 minutes to reduce liquid.

Ladle into bowls, drizzle with a little extra-virgin olive oil if desired, and garnish with additional parsley. Serve hot.