Adjust the oven rack to middle position and preheat oven to 375º
Spread the oats evenly on rimmed baking sheet and bake until lightly browned, about 10 minutes stirring after the first 5 minutes. Place sheet pan of oats on a wire rack to cool for 5-10 minutes.
Transfer half of cooled oats (4.5 ounces or 1 ½ Cups) to bowl and stir in the warm water.
Cover bowl with plastic wrap and let sit until water is absorbed, about 10 minutes.
Whisk almond flour, gluten free flour blend, salt, baking powder, xanthan gum (if using), cinnamon, and nutmeg together in medium bowl; set aside.
Whisk both sugars, melted butter, egg and yolk, oil, and vanilla together in large bowl until well combined and smooth.
Stir in flour mixture, oat-water mixture, and remaining toasted oats using a rubber spatula until well mixed and a soft dough forms.
Fold in raisins, if using.
Cover bowl with plastic and let dough rest for 30 minutes. This allows the dough to hydrate.
Preheat oven to 325°. Line a large baking sheet with parchment paper. You should have enough dough for 2 sheets of cookies.
Using a 2 tablespoon cookie scoop, place the dough 2 inches apart on prepared sheet.
Once the cookie sheet is full, form each into a ball shape, if needed.
Using damp hands, press dough to ½ inch thickness.
Bake cookies, 1 sheet at a time, 22 to 25 minutes, rotating the after sheet after the first 12 minutes.
The cookies are done when the edges are set and beginning to brown while the centers are still soft and puffy.
Remove the cookies from the oven and let them cool on sheet for 5 minutes, then transfer to wire rack. Serve warm or at room temperature.
After Cookies have cooled, place them in an airtight container and store at room temperature to keep them fresh.