Preheat oven to 325 degrees F. Use a sharp knife to score the top and bottom of roast in a diamond pattern, making cuts about 1/4 inch deep. Combine mustard, rosemary, garlic, salt, and pepper in a bowl. Rub the mustard mixture evenly onto all sides of meat. Insert a meat thermometer near the center of the roast. Place roast on a rack in a shallow pan.

Roast in the preheated oven for 1-1/4 to 1-3/4 hours or until the thermometer registers 155 degrees F. Remove roast to a platter, cover with foil, and let rest for 15 minutes.

Or, to grill pork, arrange coals for indirect grilling in a grill with a cover. Test for medium-low heat where the meat will cook. Place roast in a roasting pan on the grill rack. Cover; grill 1 to 1-1/4 hours or until meat thermometer registers 155 degrees F, adding prelit coals as necessary to maintain heat. Remove meat from grill. Cover with foil and let stand 15 minutes.

Meanwhile, for Rhubarb Sauce, stir rhubarb, orange juice, vinegar, and sugar in a medium saucepan. Bring to boiling; reduce heat. Cover and simmer about 15 minutes or until rhubarb is very tender. Serve warm.

To serve, slice the roast and serve with warm Rhubarb Sauce. Makes 8 to 10 servings.

Cover and chill any leftovers for up to three days.

1 fruit, 2-1/2 meat.