Prepare Blackberry Sauce. Preheat oven to 325 degrees F. Line a roasting pan with foil and place a rack in pan; set aside.
To butterfly roast, turn roast fat side down. Make a lengthwise cut down the center, cutting to within 1/2 inch of the opposite side. Place knife in the V of the first cut. Cut perpendicular to the first cut to within 1/2 inch of side. Repeat on opposite side of the V. Open roast flat. Sprinkle meat with salt and pepper. Spread with half the Blackberry Sauce and sprinkle with half the nuts.
Starting from a short side, roll up meat (some sauce may leak out). Place roast on rack in prepared roasting pan. Insert a meat thermometer into center of roast. Roast, uncovered, for 1 1/4 to 1 1/2 hours or until thermometer registers 145 degrees F. Tent with foil and let stand for 15 minutes.
Reheat remaining Blackberry Sauce. Spoon sauce over roast. Sprinkle with remaining nuts. If desired, top with fresh blackberries and snipped fresh rosemary.
Coat a medium saucepan with nonstick cooking spray. Cook onion in pan over medium heat for 5 minutes or just until tender. In a bowl combine onion, blackberry spreadable fruit, green jalapeno jelly, lemon peel, and soy sauce. Stir in fresh blackberries.