Combine first 4 ingredients in a medium bowl; add milk, margarine, and egg, stirring with a wire whisk until blended.
Pour oil to a depth of 2 to 3 inches into a Dutch oven; heat to 375°. Dredge pineapple slices in flour mixture. Fry pineapple slices in hot oil, 2 slices at a time, until golden, turning once. Drain well on paper towels.
Combine powdered sugar and cinnamon; sift over warm pineapple slices. Transfer slices to individual serving plates; top each with 1/4 cup Neapolitan ice cream. Serve immediately.