Combine lime juice, water, soy sauce, sesame oil, salt, and ground red pepper, if desired, in a medium bowl; stir with a whisk. Stir in green onions and ginger.
Serve this simple, versatile sauce as a zippy condiment for roast beef or pork, or drizzle it onto a platter of sliced grilled meat (especially lamb) or sliced grilled vegetables, such as eggplant or zucchini. Omit the onions and ginger, and it's delicious on cooked greens such as bok choy, mustard greens, or kale.
