How to keep the reheated Oats from sticking together

For me, I use the microwave's power setting. This is sometimes a misunderstood feature. When you don't set the power level, then it is 100%. This means during 100% of the cook time the magnetron inside the microwave is active and radiating your food. If you set the power level to 10, then during the cook time, the magnetron will not be active the entire cook time, instead it will be active during 10% of the time. "Power" is a bad term because it does not effect the power level of the magnetron. It affects the amount of time it is active.

This is helpful to know if you also understand that microwave energy does not penetrate very deeply into your food. It enters about 1 to 2 inches. This mean the surface of your food gets really hot when the magnetron is on, but the deeper parts are not getting hot. You use this to your advantage by setting a lower power level which allows the heat to conduct through your food naturally when the magnetron is not active. It is a way to warm the entire product without blasting the outside of it.

If you are microwaving something thick, then reduce the power and increase the time.

If you have a microwave safe shelf, then use it! That allows more microwave energy to come in conduct with more of your food's surface. The waves "bounce" inside the box, so being on a shelf lets some wave bounce under it and hit the bottom of your food.

(Disregard previous version: I did not notice this recipe had no wheat flour.)

This recipe gets all of its structure from oats.

Instant oats are pre-hydrolized, so that they cook faster. Regular oats are just the natural oat, perhaps cut, and rolled flat. They need more moisture and time to hydrolize.

The recipe will probably work, perhaps with a slightly different texture. They may bake faster due to the fact that the oats are already hydrolyzed.

If you choose recipe where the structure comes from wheat flour, the type of oats will matter less.