Combine first 6 ingredients in a small bowl; set aside.
Unroll roast; trim fat. Rub ginger mixture into folds and over surface of roast. Place roast in a large zip-top plastic bag; seal and marinate in refrigerator 12 to 24 hours, turning bag occasionally. Remove roast from bag; set aside.
Preheat oven to 325°.
Heat the oil in a Dutch oven over medium-high heat; add roast, browning on all sides. Add onion, wine, garlic, and broth, and bring to a simmer. Insert meat thermometer into the thickest portion of roast. Cover and bake at 325° for 50 minutes or until thermometer reaches 145° (medium-rare), basting occasionally. Remove from pan; set aside, and keep warm.
Strain cooking liquid through a sieve into a bowl, and discard solids. Return cooking liquid to pan. Bring to a boil, and cook 5 minutes or until reduced to 2 cups. Combine flour and water in a small bowl; stir well with a whisk. Add flour mixture to cooking liquid in pan. Bring to a boil; cook 1 minute or until slightly thick, stirring constantly with a whisk. Stir in Spiced Pear Butter; serve sauce with lamb.