Combine frozen peaches, 3 tbsp flour and 3 tbsp sugar in a 1.5 quart IP-friendly casserole
Pour 1 cup of water in the Instant Pot and insert the steam rack. Carefully lower the casserole on to the steam rack using a foil sling, then secure the lid, making sure the vent is closed.
Using the display panel select the MANUAL or PRESSURE COOK function*. Use the +/- keys and program the Instant Pot for 20 minutes.
Meanwhile, in a large nonstick skillet combine Topping Mixture ingredients. Cook and stir over medium-high heat for 2-3 minutes.
Dot butter pieces evenly over the oat mixture and cook, stirring constantly, just until butter is melted and fully incorporated.
Immediately turn out oat mixture onto parchment paper in a thin, even layer to cool.
When Instant Pot cooking time is up, let the pressure naturally release for 5 minutes, then quick-release the remaining pressure.
Open the lid and pour the oat topping on the peaches. Arrange in an even layer, pressing down lightly to get good contact with the peaches. Allow mixture to set for 5-10 minutes.
Remove casserole from Instant Pot. Serve warm sprinkled with cinnamon.