1. In a saucepan coated lightly with oil over high heat, sauté the onions and ginger until soft, about 5 minutes. Add the orange zest and juice, soy sauce, grapefruit juice, and sugar and bring to a simmer.
2. Reduce by 50 percent over low heat, about 10 to 15 minutes.
Check for flavor. Immediately transfer to a blender and blend until almost smooth. Drizzle in oil. Do not blend until super smooth.
3. Bring to room temperature, transfer to a glass jar, seal and store in refrigerator for up to two weeks.
Makes 2 cups