In a small mixing bowl, add ¼ cup tapioca starch and ¼ cup water. Stir well until a smooth, paste-like consistency forms.
Mix in 1 teaspoon of plain, unsweetened Greek yogurt. If you prefer a creamier or slightly thicker icing, increase to 2 teaspoons. Stir in 1 teaspoon of honey to slightly sweeten and bind the mixture.
Whisk or stir until everything is fully blended and the icing is lump-free. The final texture should be thick but spreadable. If it’s too runny, add a bit more tapioca starch; if it’s too thick, add a drop or two of water.
Use a spatula, spoon, or piping bag to apply the icing onto cooled dog cookies. Let cookies sit at room temperature or refrigerate until the icing sets (usually 20–30 minutes).