Use the leftover lamb from this meal in a stir-fry, stew, or sandwich.
Preheat oven to 500°.
Unroll roast; trim fat from roast. Reroll roast; secure at 1-inch intervals with heavy string. Make 6 (1/2-inch-deep) slits in roast; place garlic halves and rosemary into each slit. Sprinkle with 1/2 teaspoon salt and pepper. Place roast on a broiler pan; insert meat thermometer into thickest portion of roast. Bake at 500° for 10 minutes. Reduce oven temperature to 425° (do not remove roast from oven).
Combine 1/4 teaspoon salt, 1 teaspoon olive oil, and squash, and arrange squash around roast. Bake at 425° for 22 minutes. Combine 1 teaspoon olive oil, 1/4 teaspoon salt, broccoli spears, and the minced garlic. Carefully turn roast, and arrange the broccoli mixture around the roast. Bake at 425° for an additional 25 minutes or until thermometer registers 145° (medium-rare). Let roast stand for 5 minutes.