Beat the egg with the milk. Arrange the flour, egg mixture, and panko in three shallow dishes. Dust each scallop lightly with the flour (shake off excess), coat with the egg, and dredge in the panko.
Heat the oil in a large nonstick skillet over medium heat until it just begins to shimmer. Add the scallops and cook 2 to 3 minutes undisturbed, until golden. Turn and cook 2 minutes more, or until cooked through.
Plate and garnish with lemon wedges, if desired. Serve with prepared mashed potatoes and sauteed baby spinach.