VEGGIEPREP: Thinly slice the avocado, cut the cucumber into matchsticks, thinly slice the red pepper.
TUNA: Thoroughly drain the tuna. Flake with a fork and place in a large bowl. Add in the mayo, Sriracha, lime zest, lime juice, and white sugar. Add in a pinch of salt and pepper to taste (I add a heaping 1/4 teaspoon fine salt and 1/8 teaspoon pepper) and gently stir to combine. Once combined, set aside.
ASSEMBLY: Lay out 4 tortillas. Divide the tuna mixture evenly among the tortillas. Top the tuna with even amounts of avocado, carrots, cucumber, red pepper, and if desired, a few sprigs of cilantro. Top each with a generous sprinkle of salt and pepper (or to taste) and another drizzle of fresh lime juice, if desired.
ENJOY: Roll up tightly and enjoy immediately. (Do not make these in advance; the tuna will get the tortilla soggy.)