Preheat oven to 425 F. Pierce a sweet potato with a fork and bake for 50-60 minutes, or until soft and tender when pierced with a fork. Transfer cooked sweet potato flesh to a large bowl and mash.
Add the grated apple into the bowl with the mashed sweet potato.
Add the egg, oat flour, cinnamon, and salt (if using). Mix to combine.
Heat the oil over medium-high heat. Fry heaping tablespoons of the mixture until golden and crispy, about 2-3 minutes per side. You may wish to flatten the fritters with the spatula once flipped to help it cook through in the center.
Alternatively, you can bake the fritters in the oven on a well greased baking sheet at 425 F, for 20 minutes flipping halfway through.
Serve warm or at room temperature, alone or with your favourite dip.