Shred the carrot using a cheese grater. Slice the green onion.
Add the carrot, green onion, brown sugar, olive oil, apple cider vinegar, cayenne, garlic powder, smoked paprika, salt, and some freshly cracked pepper to the bowl with the drained tuna.
Stir everything to combine, then let the mixture sit for about five minutes to allow the flavors to blend. Serve immediately, or refrigerate until ready to eat.