In large nonstick skillet, heat oil over medium-high heat. Add garlic; cook, stirring occasionally, 1 minute. Add broccoli, salt and red-pepper flakes; cook, stirring occasionally, until crisp-tender, 7 to 8 minutes. Keep warm.
Meanwhile, place chicken on flat work surface; season with salt, Italian seasoning and black pepper. Place 2 sage leaves on each piece; cover each with 1 ounce of prosciutto. With the sharp side of a chefs knife pointed up, gently pound chicken so prosciutto adheres to chicken.
In large nonstick skillet, heat oil over medium-high heat. Place chicken, prosciutto side down, in skillet; cook until prosciutto is nicely seared, 2 to 3 minutes. Turn chicken over; cook until internal temperature registers 170°F on instant-read thermometer, about 2 minutes. Remove to a warm plate.
Off heat, add marsala wine to skillet. Return to heat; scrape up any browned bits from bottom of skillet. In small bowl, stir together beef broth and cornstarch. Add to skillet. Bring to simmering; simmer until thickened, 1 to 2 minutes. Remove from heat.
To serve, spread broccoli on a large serving platter. Place chicken on top and spoon sauce over chicken. Serve with buttered orzo on the side, if desired.