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Turn the oven on and adjust the temperature to the correct setting so the oven starts the preheating process. When the preheat light has switched off, this means that the oven is heated to the right temperature and that it's ready to use. Some ovens don't have a light that indicates when the oven has preheated. In this case, letting the oven heat up for around 15 minutes is usually sufficient. Get a baking tray that fits into your oven. Then cut or tear a piece of parchment paper that is large enough to fit the tray. Line the baking tray with the parchment paper to keep the tuna cat treats from sticking. Alternatively, you can use a silicone baking mat instead of parchment paper.
Preheat the oven and set the temperature to 350F (177C). Place a sheet of parchment paper over a baking tray.