Preheat oven to 230 degrees C (450 F). Line two baking sheets with aluminum foil (for easy cleaning) (*see footnote 1). Spray an even layer of oil onto the foil.
Halve potatoes crosswise if using very large potatoes. Slice into 1-cm (1/3-inch) thick pieces, and then cut into 1/2-cm (1/6-inch) wedges.
Spread the potatoes onto the lined, oiled baking sheet. Do not crowd the potatoes, otherwise they will be steamed instead of fried. Generously spray oil on top of the potatoes (very important, otherwise your fries will dry up instead of turning crispy). Sprinkle sea salt and Japanese red pepper mix onto the potatoes.
Bake until the bottom of the potatoes is charred, 25 to 30 minutes. Stir the potatoes once. Return to the oven and bake for another 15 minutes.
Mix Greek yogurt, honey, soy sauce, and Sriracha in a small bowl.
When the fries are cooked, let them rest for 5 minutes to cool. This step will further crisp up the fries. Sprinkle green onions on top (if using) and gently mix a few times with a spatula.
Serve warm with the dipping sauce.