Prik Nam Pla starts with a base of fish sauce, lime juice, and rice vinegar. It is spiked with Thai chilis and sweetened with sugar. It's a perfect dipping sauce for Thai Fish Cakes, crispy fried spring rolls, or any meat or seafood.
Combine the sugar, fish sauce, vinegar, lime juice, garlic, and chili in a food processor and process until smooth and well combined.
Transfer the mixture to a small bowl, add the cucumber, if using, and stir to mix. Garnish with the peanuts, cilantro, and additional chili slices, if desire.