If you’re planning to cook these right away, pre-heat your oven to 425 °F.
Wash or wipe clean the portobello caps with a damp cloth or paper towel. You can gently remove the dark gills with a spoon if you’d like, but I usually don’t mind them. Slice the caps into 1/4-inch thick slices.
Get ready to bread the mushroom slices: Place the flour, eggs, and panko into three separate bowls. Beat the eggs until smooth. To the bowl with the panko breadcrumbs, add the garlic powder, black pepper, paprika, and salt, and stir to combine.
In assembly line fashion, bread each mushroom slice by dredging in the flour, then the egg, then the panko, being sure to shake off any excess at each step. This process (and your hands!) stays much cleaner if you use one hand for the flour and eggs and the other hand for the panko.
Place the breaded mushrooms onto a parchment-lined baking sheet.
*If you are making these ahead, you’re done! These breaded mushrooms can hold in the fridge for up to 12 hours before continuing with the steps below, or transferred to the freezer.
When ready to cook the fries, mist or lightly drizzle olive oil onto both sides. Bake 10 to 12 minutes, flipping the fries halfway through baking, until golden brown and crisp. If starting from frozen, baking time will likely take 15-20 minutes total.