Sauté onion and bell pepper in hot oil in a large skillet over medium-high heat 5 to 7 minutes or until tender. Remove from heat. Add rice and next 5 ingredients; stir in egg. Set stuffing aside.
Butterfly pork loin roast by making a lengthwise cut down center of 1 flat side, cutting to within 1/2 inch of bottom. From bottom of cut, slice horizontally to 1/2 inch from left side; repeat procedure to right side. Open roast, and place between 2 sheets of heavy-duty plastic wrap; flatten to 1/2-inch thickness using a meat mallet or rolling pin.
Spoon 1 1/2 cups stuffing evenly over roast, leaving a 1/2-inch border. Roll up; tie with string at 1-inch intervals. Place, seam side down, in a lightly greased 11- x 7-inch baking dish.
Bake at 375° for 55 to 60 minutes or until a meat thermometer inserted in center registers 160°. Reheat remaining hopping John, and serve with roast.