Preheat oven to 425 degrees Fahrenheit.
Meanwhile, prepare the kohlrabi. If they have stems/leaves attached you can remove and discard. Remove the tough end. Note: If you like, you can reserve the kohlrabi leaves for use in another recipe.
Carefully cut each kohlrabi in half, remove/discard core (if necessary) and peel. Turn each half down so the large flat portion is on the surface and cut into ½-inch slices. Then cut those slices into fries, about ⅓-inch to ½-inch thick (refer to the body of the post above, if necessary).
Place kohlrabi fries in a clean tea towel to remove any excess moisture (optional).
Place kohlrabi fries in a bowl and toss with 2.5 tablespoons of avocado oil, garlic powder (if using), ancho chili powder, black pepper and salt, ensuring the kohlrabi fries are well coated with the oil and seasonings.
Grease a large sheet pan (or two smaller ones) with the remaining ½ tablespoon of avocado oil.
Place the kohlrabi fries onto the prepared sheet pan and spread them out in a single layer. Bake the fries for 15 minutes, then remove the sheet pan from the oven and flip the fries with a spatula (again, try to ensure that the fries are in a nice, even layer so they bake up nicely). Place the sheet pan back in the oven and continue baking the fries for another 15 minutes or until the outside of the fries is golden brown and they're tender inside.
Transfer kohlrabi fries to a serving dish. Garnish, if desired, with green onion. Serve and enjoy!