Cut the onion, carrot, potato, celery stalks, and green pepper into cubes.

Sauté the onion in a pot.

Add the remaining cubed vegetables to the pot and sauté.

Pour in water and vegetable stock or chicken bouillon.

Bring the mixture to a simmer and cook until the vegetables are almost done.

Add tomato paste and chopped parsley to the soup.

Season with salt, pepper, and lemon juice to taste, adding the lemon juice gradually to avoid making the soup too sour.