In a medium bowl, whisk together the peanut butter, mayonnaise, fish sauce, lime zest and juice, smoked paprika, and gochugaru, if using, until smooth and well combined.
Add the sliced cucumbers and toss until the cucumber rounds are evenly coated in the dressing. Taste and season with salt, if needed.
Top with chili crisp and/or toasted sesame seeds, if using, and serve immediately.
