Wash okra and drain. Remove tips and stem ends. Cut okra crosswise into 1/2 inch slices.
Combine egg and buttermilk. Add okra, stirring to coat well. Let stand 10 minutes.
Combine cornmeal, flour, baking powder and salt in a zip-top plastic bag.
Drain okra. With small portions at a time, using a slotted spoon, place okra in bag with cornmeal mixture, shaking gently to coat.
Brush oil on a 15x10x1 inch jellyroll pan; add okra in a single layer.
Coat okra with cooking spray and bake in a 450 degree oven for 8 minutes. Stir well and spray with cooking spray again; baking 8 additional minutes. After last baking, broil 4 inches from heat (with electric oven door partially opened) 5 minutes or until browned, stirring occasionally.