Preheat oven to 450 F. Lightly grease two baking sheets and place them in the oven to preheat.
To make the flax egg, mix the flax and water together in a small bowl and let it sit in the fridge for 20-30 minutes until it reaches a gloopy egg-like consistency.
Place the oats in a small food processor and pulse until they reach a flour-like consistency. In another bowl, mix together the oat flour, salt, pepper and chili.
Add the chex cereal to the food processor and pulse until it breaks into crumbs. Transfer to a third bowl.
Dip the fish filets into the flour, then transfer them to the flax egg until well coated. Finally, coat them in the Chex panko crumbs. Transfer to one of the preheated baking sheets.
Meanwhile, mix the potatoes with the oil, sea salt, pepper and chili. Transfer to the other large baking sheet in a single layer and bake for 25 to 30 minutes, turning once for even browning.
About 15 minutes into your sweet potatoes cooking, add in a second sheet with the fish and bake for about 12 to 15 minutes or until cooked through and just slightly starting to brown. Chex, like panko, doesn’t get super golden brown so you’ll likely just see a slight golden hue.
While still hot, top the fish and chips with a pinch of fleur de sel.