If using an air fryer, proceed to step 2. If using a regular oven, preheat oven to 350°F degrees. Butter a baking dish that is big enough to hold your peaches and set aside.
Using a melon baller, scoop out and discard the red flesh from the center of each peach, create a cavity large enough to hold streusel but leave enough flesh to give the peach stability.
Combine flour, sugars, cinnamon, salt, pecans, and oats. Add in diced butter and use your fingers to rub the butter into the dough until the mixture is crumbly and the butter is pea sized or smaller. If you'd prefer you can do this in a stand mixer with the paddle attachment to mix up the filling. Divide the filling between the peaches, packing it into each cavity.
AIR FRYER: Place the stuffed peaches, cut side up, in the air fryer. Turn the temperature to 350°F and cook for about 5-15 minutes, until the topping is lightly browned and the peaches have softened but are still holding their shape. Start checking them after 5 minutes, give them a squeeze to see how soft the peaches are. Depending on how ripe and how large your peaches are the cook time will vary a bit. Allow to cool slightly. Serve warm with vanilla ice cream.
OVEN: Place peaches cut side up in your baking dish. Bake peaches for 35-45 minutes, until the topping is lightly browned and the peaches have softened but are still holding their shape. Allow to cool slightly. Serve warm with vanilla ice cream.