Wash chicken breast and pat dry. Remove and discard all fatty parts and tendons. Cut into 3/4 inch cubes. Place in a small saucepan with salt, pepper, rosemary leaves, and garlic. Toss to distribute the seasoning evenly. Add all the oil and set aside in the refrigerator for several hours or overnight.
Place on moderately high heat and brown for 10 minutes, stirring frequently. Add the broth and let the steam bring the flavors together for 1 minute. Add lemon juice and remove from heat. Serve with its gravy and spinaci all'agro.