Place a medium, non-reactive saucepan over a medium-high setting, pour in the oil and let it come up to frying temperature.
Sauté the onions, stirring, until they become translucent. Add the tomatoes, orange juice and zest, sugar, salt and basil. Stir and let the mixture come to a boil. Reduce the heat to low and simmer the mixture for about 25 minutes.