In a large saucepan, lightly fry the leeks or onions in olive oil, add the minced meat and fry with them. Add the carrots, garlic, potatoes and mushrooms and roast briefly. Add the tomato paste and toast briefly as well. Skin and chop fresh tomatoes and add to the pot, alternatively add the pizza tomatoes.
Pour on enough water to cover everything. Stir in the vegetable stock, bring everything to a boil and season with salt, pepper and possibly soy sauce. Let simmer for 25-30 minutes.