Place lentils and 3/4 cup water into a saucepan and bring to the boil. Simmer for approximately 20 minutes.
Preheat oven to 180C. Cover a baking tray with foil and spray lightly with olive oil spray.
To prepare chicken breasts, take each breast and place on chopping board. Cover with a sheet of baking paper and using a meat hammer or rolling pin, flatten each breast to a thickness of approximately one centimetre.
Heat oil in frypan. Add prosciutto, onion, garlic and sage. Cook stirring frequently, until onion is soft. Stir in lentils and spinach leaves. Season with lemon juice and pepper to taste. Set aside.
On each chicken breast, spread 1/4 of the lentil mixture across the whole breast and roll up from the shortest side.
Carefully lift each breast onto the prepared baking tray, seam side down. Spray each breast lightly with olive oil spray, cover tray with foil and place in oven.
Cook for 30 minutes covered, then uncovered for 5-10 minutes to brown chicken.
Cut each breast into 5 'wheel' slices to serve. Pour any remaining juices over each breast.
For an elegant hors d’oeuvre, slice chicken pinwheels finer and place on miniature toasts with a dollop of whole egg mayonnaise or tomato chutney.