Cube the tofu & drain for 10 minutes in a colander. Heat the vegetable oil in a wok over medium heat. Stir-fry the onion for 2 minutes. Add the tofu, spreading it evenly in the bottom of the wok & fry until it begins to change colour. Turn over & repeat. Remove tofu. Add the curry paste & stir-fry for 1 minute. Put the tofu back in the wok & add the okra & tomatoes. Stir-fry taking care not to break the tofu, for 3 to 4 minutes. Add the dissolved cornstarch with the lime juice, salt & soy sauce. Let the mixture cook, stirring occasionally for 5 to 7 minutes. Garnish with the green onion & serve hot over the rice.