Combine breadcrumbs with ¼ cup water and sage in a small bowl. Lay prosciutto slices on a board, slightly overlapping, to same length as pork fillet. Spoon breadcrumb mixture along centre. Top with pork fillet and wrap with prosciutto to enclose mixture. Use toothpicks to secure if necessary.
Heat 1 teaspoon of oil in a non-stick frying pan on medium. Fry extra sage leaves for 30 seconds. Drain on paper towel and set aside. Add pork fillet to same pan and cook for 3-4 minutes, turning, until browned all over. Add potato and zucchini. Drizzle with remaining oil and season to taste.
Cover and continue to cook for 5-7 minutes, until pork is done to taste. Remove and rest in a warm place for 5 minutes. Meanwhile, return vegetables to heat and continue to cook, if necessary, until golden and tender, tossing frequently.
To serve, slice pork and arrange on plates with vegetables. Top with fried sage leaves.