In our version of the classic New Orleans po'boy, chewy ciabatta replaces the usual French bread. These crisp oysters fry for a few seconds per side; anchovy fillets amplify the oysters' oceanic flavor.
Preheat oven to 400 degrees. Melt butter in a saucepan with garlic. Puree in a food precessor; set aside. Remove some of the bread from inside rolls. Place rolls on a baking sheet, cut sides up; set aside.
Whisk flour, powdered milk, cayenne, salt, and herbs in a bowl; season with pepper. Dredge oysters in mixture. Heat 1 inch oil in a large skillet over medium-high heat. Meanwhile, spoon 2 teaspoons garlic butter over each roll. Bake until golden brown, about 5 minutes.
Fry oysters in batches until golden brown, 30 to 45 seconds per side. Transfer to paper towels. Sandwich oysters, arugula, anchovies, and lemon with rolls.