Preheat oven to 350°F (175°C) and line a large baking tray with parchment paper.
Add the oats to a food processor and process until they are a coarse flour-like consistency.
Add the cooked sweet potato and the coconut oil (doesn't matter if it's hard or liquid) and process until well combined.
Add the water 1 tablespoon at a time, pulsing a few times in between each addition, until the mixture can be squeezed into a firm, pliable dough with your fingers,
Remove the blade, tip out the dough and knead together a bit so it's all in a big ball.
Roll out to about 3 to 4 mm thick. I like to roll mine out on a silicone baking mat but if you don't have one you might need to sprinkle some flour on the surface to stop the dough sticking. If your dog is wheat intolerant be sure to use oat flour (just process a few more oats until they are flour).
Cut out into cookie shapes using a cookie cutter or just cut the dough into even pieces with a knife or pizza cutter.
Carefully transfer the cookies to the lined tray and bake in the oven for 20 - 25 minutes. Keep an eye on them towards the end as all ovens and baking trays cook differently. The cookies should be very hard and dry with slightly golden bottoms.
Cool completely on the tray then store in an airtight container.
Video
Notes
Cookies will keep for 2 months in an airtight container at room temperature or up to 6 months in the freezer.