To make the batter, place all the ingredients in a bowl and whisk until a smooth batter forms. It should have the consistency of thick pancake batter. Cover and refrigerate. To make the dressing, place all the ingredients in a bowl, season with salt and whisk together.
Fill a large saucepan or wok two thirds full of oil and heat to 180°C.
Working in batches, dust the wahoo in flour, then dip in the batter, allowing the excess to drip away, and then deep-fry, turning occasionally, until golden and crisp. Don’t overcrowd the pan or the temperature of the oil will drop, making the fish oily. Drain on paper towel.
To serve, arrange the guava on serving plates and tear some basil over the top. Drizzle with a little vinaigrette, then top with the fish and serve immediately with lime wedges.