Pound chicken breasts with the flat side of a meat mallet or the bottom of a glass until thin.
Either in a mortar or on a small plate, combine first 7 ingredients. Grind together ingredients with a pestle or the bottom of a glass.
Coat chicken lightly with olive oil. Use spice mixture to coat chicken evenly; place in the refrigerator until needed.
In a saucepan over medium-high heat, melt butter. Add prosciutto, shallots, and garlic and sauté for 30 seconds. Add Marsala to pan and simmer for 30 seconds. Add mushrooms and black pepper and simmer for 5 minutes, stirring occasionally. Reduce heat to medium.
Dissolve corn starch in chicken broth, then add to saucepan. Simmer for 5 minutes, stirring often.
Add parsley and cream to saucepan and simmer for 3 - 4 minutes, or until thick. Remove from heat and cover until needed.
Grill coated chicken over a medium flame for 5 - 7 minutes per side, or until cooked through.
Place grilled chicken on individual serving plate and spoon sauce over chicken.