Dice the onion, carrots, celery, and zucchini into small, evenly sized pieces. Mince the garlic, drain and rinse both cans of beans, and roughly chop the spinach. Keeping the vegetables similar in size helps them cook evenly and ensures each spoonful contains a balanced mixture of ingredients.

Heat 2 tablespoons (30 ml) extra-virgin olive oil in a large 6-quart Dutch oven or soup pot over medium heat. Add the diced onion, carrots, and celery. Cook for 6 to 8 minutes, stirring occasionally, until the onion becomes translucent and the vegetables begin to soften. The vegetables should look glossy and tender around the edges without developing deep brown spots. Reduce the heat slightly if they begin to brown too quickly.

Stir in the diced zucchini and cook for 3 minutes, allowing it to soften slightly. Add the 4 minced garlic cloves and cook for another 30 to 60 seconds, stirring frequently. The garlic should become fragrant but should not turn dark brown, which can introduce bitterness.

Add 2 tablespoons (30 g) tomato paste to the vegetables. Stir continuously for about 1 minute, until the paste coats the vegetables and deepens slightly in color. This brief cooking step helps mellow the raw taste of tomato paste and creates a richer foundation for the soup.

Pour in the can of diced tomatoes with its juices, 6 cups (1.4 liters) vegetable broth, and 1 cup (240 ml) water. Add 1 teaspoon dried Italian seasoning, 1 teaspoon dried basil, 1/2 teaspoon black pepper, and 1/2 teaspoon fine salt. Stir thoroughly, scraping the bottom of the pot to release any flavorful tomato paste or vegetable bits.

Increase the heat to medium-high and bring the soup to a gentle boil. Reduce the heat to medium-low, cover partially, and simmer for 10 to 12 minutes, until the carrots are nearly tender when pierced with a fork. The broth should bubble gently rather than boil rapidly. A vigorous boil can break down the vegetables and evaporate too much liquid.

Stir in the drained cannellini beans, drained kidney beans, and 3/4 cup (105 g) dry ditalini pasta. Increase the heat slightly if needed to bring the soup back to a gentle simmer. Cook uncovered for 8 to 12 minutes, stirring occasionally, until the pasta is tender but still has a slight bite and the carrots are fully cooked. Check the pasta package for its recommended cooking time. If the soup becomes too thick, add a little additional hot water.

Add 2 cups (60 g) roughly chopped baby spinach and stir gently. Cook for 1 to 2 minutes, just until the spinach wilts and turns bright green. Avoid simmering the spinach for too long, as it can lose its fresh color and become excessively soft.

Turn off the heat and stir in 1 tablespoon (15 ml) fresh lemon juice. Taste the broth and adjust the salt if necessary. The soup should have a balanced flavor with noticeable tomato richness, savory herbs, and a gentle brightness from the lemon. If the broth tastes too concentrated, add a small amount of hot water to loosen it.

Ladle the hot soup into bowls, making sure each serving contains vegetables, beans, pasta, and broth. If desired, garnish with freshly grated Parmesan cheese and chopped parsley. Serve immediately while the pasta is tender and the vegetables retain their texture.