In a large bowl, combine turkey, scallions, soy sauce and five-spice powder; form into 4 patties.
Heat a large nonstick skillet over medium-high heat. Add burgers and cook 3 minutes per side or until internal temperature reaches 160°.
Combine mayonnaise and sriracha; spread 11/2 tsp over bottom half of each bun. Place burger on bun and evenly divide remaining mayonnaise mixture over each burger. Add lettuce, onion and bun tops.
Serve with Sweet Potato Fries (recipe below), if desired.