Begin by warming the olive oil in a large, heavy-bottomed soup pot set over medium heat. Once the oil shimmers, add the chopped onion and minced garlic. Sauté gently for 5 to 7 minutes, stirring often, until the onions turn translucent and aromatic.

Introduce the diced carrots, celery, potatoes, courgette, and red bell pepper to the pot. Give everything a good stir to coat the vegetables in the fragrant oil and cook for another 5 minutes. This helps the vegetables begin to soften and release their flavors.

Next, pour in the canned tomatoes along with their juices, followed by the vegetable stock. Add the dried thyme and the bay leaf. Season generously with salt and freshly ground black pepper, then stir to combine all the ingredients.

Bring the mixture to a boil, then immediately reduce the heat to a gentle simmer. Cover the pot loosely and let the soup cook for 20 to 25 minutes, or until all the vegetables are tender and the flavors have melded beautifully.

Once the vegetables are fully cooked, taste and adjust the seasoning if needed. Remove and discard the bay leaf.

Ladle the hot vegetable soup into bowls and garnish with chopped fresh parsley if desired. Serve immediately with slices of crusty bread or a crisp green salad on the side.