In a large bowl, combine squash, carrots, onion, and cilantro. Season with salt and pepper.
Season shrimp with salt and pepper, then add to the vegetables. Toss to combine.
In a separate bowl, combine rice flour, baking powder, fish sauce, and water until smooth.
Pour the batter over the shrimp and vegetables. Toss until evenly coated.
Heat about 1 inch of oil in a deep pan over high heat.
Scoop ½ cup of the mixture onto a large spoon or turner, then carefully slide it into the hot oil.
Fry for about 2 minutes per side, or until golden brown and crisp. Drain on paper towels.
In a small bowl, combine vinegar, sugar, shallot, and chilies. Season with salt and pepper.
Serve the ukoy warm with the spiced vinegar on the side.