Cut onion into thin rounds. Cut peppers into thin rounds. Finely mince garlic. Put olive oil into frying pan; add onion and pepper rounds, garlic and tomato. Season it with chili salt and pepper. Sauté it for about 40 minutes. During the process add some water to prevent premature burning. The sauce is ready to serve when all liquid evaporates; vegetables are soft and reduced in size. Serve hot.