Cook the gnocchi in a large saucepan of gently simmering water following packet directions. Drain. Rinse under cold water. Drain well.
Heat 2 tablespoons oil in a large, deep frying pan over medium heat. Add onion and garlic and cook, stirring often, for 5 minutes or until soft. Add mushrooms and cook, stirring occasionally, for 4 minutes or until softened. Add stock and bring to boil. Boil gently for 5 minutes. Stir in cream, reduce heat to medium and simmer gently 5 minutes or until sauce is reduced slightly. Season to taste.
Heat remaining oil in a large frying pan over medium-high. Add sage and cook for 2-3 minutes then remove to a plate. Increase heat to high, in two batches, add gnocchi to pan and cook 2 minutes or until golden on both sides.
Return all gnocchi to pan. Add spinach and mushroom sauce, stir to coat gnocchi. Serve gnocchi topped with sage leaves.