In a heavy saucepan over medium heat, warm the oil. Add the onion and sauté until just soft, about 3 minutes. Put the tomatoes on top of the onions and then add the okra. Sprinkle the sugar, salt, and pepper over all. Bring the mixture to a boil, cover, and cook, stirring occasionally, until very tender and thick, about 1 hour or so. Add water if necessary to keep the pan from going dry. The dish will become a thick, stewy mélange when ready. Taste and adjust the seasoning, then serve.