In a large bowl, mix the graham cracker crumbs, powdered sugar, and melted butter until the mixture holds together when squeezed.
Grease a muffin tin generously with olive oil spray.
Press the crust firmly into the bottom and slightly up the sides of 6 muffin cups. Press hard — compacted crust is what keeps the cups intact.
Air fry at 300°F for 7–12 minutes, until the crust is lightly golden and smells toasted.
Press a marshmallow half, cut side down, into each cup.
Return to the air fryer at 390°F for 1–2 minutes (or use the broil setting), watching constantly, until the marshmallows are golden brown. Remove immediately.
Press a chocolate square into the center of each hot marshmallow.
Cool in the tin for 20 minutes before removing. Serve.