In a small bowl combine margarine or butter, mustard, tarragon, the 1/4 teaspoon salt, and the black pepper; set aside.
Remove skin from turkey; set aside. Lay one turkey breast half, on work surface. Make 4 to 5 shallow cuts in the thickest portion of breast (do not cut through). Place turkey breast between two pieces of plastic wrap. Using the flat side of a meat mallet, lightly pound turkey breast to an even thickness (about 3/4 inch). Remove plastic wrap. Repeat with remaining turkey breast. Dot breast halves with half of the margarine mixture; set remaining mixture aside. Top turkey evenly with red peppers and parsley. Starting with a short side, roll up each turkey breast into a spiral. Wrap reserved skin around each roll. Tie with 100-percent-cotton string. Place on a rack in a shallow roasting pan.
Melt remaining margarine mixture and brush over surface of turkey. Insert a meat thermometer into the center of one of the turkey rolls. Roast in a 325 degree F oven for 1-1/2 to 1-3/4 hours or until juices run clear and the thermometer registers 170 degrees F.
Meanwhile, snap off and discard woody bases from asparagus. If desired, scrape off scales. In a large bowl toss asparagus, oil, and the 1/4 teaspoon salt together. Add asparagus to the roasting pan around the turkey the last 15 to 20 minutes of roasting time. Cover turkey and asparagus; let stand 15 minutes before slicing. Serve turkey with asparagus. Makes 8 to 10 servings.