1. Combine mustard, coriander, peppercorns and thyme in food processor or blender; process 1 minute or until seeds are coarsely crushed. Set aside.
2. Sprinkle salt over chopped garlic and press with side of knife against board to form a paste. Add parsley and mix until combined.
3. Rub lamb with oil then spread with garlic-parsley paste. Press spice mixture onto meat. Place in a shallow dish covered with plastic wrap or in a 2-gallon resealable plastic storage bag. Seal and refrigerate 4 hours or overnight.
4. Heat oven to 450 degrees F. Place lamb in a 17x11-inch roasting pan. Roast lamb 15 minutes. Reduce heat to 350 degrees F. Roast 1-1/4 to 1-1/2 hours more or until meat thermometer inserted in center of roast reaches 140 degrees F for medium-rare. Transfer to cutting board; cover loosely with foil. Let stand 15 to 20 minutes before slicing.
5. Serve sliced lamb with Port Gravy. Makes 8 servings.
1. Meanwhile, spoon off fat from roasting pan; pour water into pan and bring to a simmer, scraping up browned bits. Pour into small saucepan; keep warm. In cup, stir port with flour until smooth. Whisk into saucepan. Cook 1 minute until gravy thickens. Makes about 1 cup.