Heat the oil in a pan over a moderate heat, and fry the onion and garlic gently for 3-4 minutes, until softened but not browned.
Add the okra, and continue to cook gently for a further 4-5 minutes, until beginning to soften.
Add the chopped tomatoes, tomato puree or ketchup, salt, pepper, sugar, herbs, and lemon juice.
Add about 1/2 cup of water or tomato juice, just enough to half cover the vegetables in the pan, and simmer for 20-30 minutes, until the okra is tender.
Taste the sauce and adjust the seasoning if necessary.