1. Combine all the dipping sauce ingredients together in a small bowl. Thin out with about 1 teaspoon water, if necessary. Set aside.
2. Pour the oil into a deep skillet to a depth of 2-inches. Heat over medium-high heat until temperature reaches 350 F on a candy thermometer. Meanwhile, combine the flour and salt together in a medium bowl. Slowly add the seltzer water, whisking constantly, until a smooth batter forms.
3. Working with a few pieces at a time and in small batches, dip the seafood and vegetables in the batter, allowing excess to drain off, and deep-fry until batter turns golden brown and seafood and vegetables are cooked through, about 1 ½ minutes per batch. Drain on paper towels.
4. Serve warm with the dipping sauce on the side.
