Cook the oven fries according to the packet instructions. Gently heat the peanut satay sauce in a small saucepan while the fries are cooking. Once cooked, sprinkle sea salt flakes onto the fries and gently toss, then spoon them into a paper cone. Dollop a generous large spoonful of mayonnaise on top, followed by an equally big spoonful of peanut satay sauce. Top with diced white onion and serve immediately.