Pour oil into roasting pan. Place pan on lowest rack in oven while heating to 450°F.
Meanwhile, line jelly-roll pan with foil. Lightly coat with cooking spray. On sheet of waxed paper, combine flour, crab seasoning, 1/2 teaspoon salt and cayenne. In small bowl, beat egg whites until stiff, glossy peaks form. On second sheet of waxed paper, combine crumbs, chili powder and 1 teaspoon oregano.
Dip fillets into flour mixture to coat both sides. Working with one fillet at a time, spread beaten whites on one side. Cover egg white side with crumb mixture. Repeat with whites and crumbs on other side. Place on foil-lined baking pan.
When oven is heated, add potatoes, garlic, remaining 1/2 teaspoon oregano, remaining 1 teaspoon salt and the black pepper to hot roasting pan; toss to coat potatoes. Return to oven. Place fish on pan in middle rack in oven.
Bake in 450°F oven until fish is crisp and cooked through, 15 minutes; remove from oven and keep warm. Bake potatoes another 5 minutes or until tender and browned.