In a small bowl, mix together the rosemary, basil, black pepper, sugar and garlic salt. Use to season the chicken, let sit for 5 minutes.
Dredge each piece of chicken in cornflour, then coat in beaten egg and then breadcrumbs. Set the chicken onto a plate and chill for 15 minutes.
Meanwhile, make the sauce. In a small bowl, mix together the water, mustard, ketchup, vinegar and sugar. Set aside.
Heat a large frying pan with 125ml oil over high heat. Fry the chicken until light brown in colour, 3-5 minutes. Reduce the heat to medium-low and continue to fry the chicken, until fully cooked, about 3-5 minutes or until the juices run clear. Drain and transfer to a serving plate.
Heat the same frying pan with 1 tablespoon oil over high heat. Stir-fry the onion with 1 teaspoon salt until soft, 3-4 minutes. Stir in the tomatoes, sugar and sauce, mix well. Pour the sauce over the chicken or serve on the side.