1.Place 2 sage leaves along each slice of prosciutto. Wrap 1 prosciutto slice around each pork fillet; secure with toothpicks.
2.Cook pork on a heated oiled grill plate (or grill or barbecue), over medium-high heat, turning, for 10 minutes or until browned all over and cooked as desired. Remove from pan; cover to keep warm.
3.Meanwhile, heat oil in a medium frying pan over high heat. Cook the remaining sage for 30 seconds or until crisp. Remove from pan with a slotted spoon; drain on paper towel. Reduce heat to medium-high. Cook mushrooms, onion and garlic in same pan, stirring occasionally, for 4 minutes or until mushrooms are golden and tender. Add the stock and paste; bring to the boil. Reduce heat; simmer, for 5 minutes or until sauce thickens slightly.
4.Meanwhile, microwave spinach on HIGH (100%) for about 1 minute or until hot. Place spinach in a fine sieve; squeeze out excess water. Heat mash according to packet directions; transfer to a large bowl. Stir spinach into mash; season.
5.Serve thickly sliced pork with mash and mushroom sauce; sprinkle with crisp sage leaves.