Combine okra, vinegar, and 1/8 teaspoon salt in a bowl. Let stand 1 hour, stirring occasionally.
Heat oil in a medium nonstick skillet over medium-high heat. Add onion, and sauté for 7 minutes or until tender. Stir in 1/8 teaspoon salt, tomato, sugar, and pepper. Reduce heat, and simmer for 15 minutes. Add okra mixture, and cook for 40 minutes or until tender, stirring occasionally. Stir in parsley.