To brine pork, combine first 6 ingredients in a large nonaluminum bowl or pan, stirring until sugar and salt dissolve; add pork. Cover and refrigerate 8 hours or overnight. Remove pork from brine; discard brine.
Preheat oven to 325°.
Starting off-center, slice pork lengthwise, cutting to, but not through, other side. Open uneven portions, laying pork flat. Turning knife blade parallel to surface of cutting board, slice larger portion of pork in half horizontally, cutting to, but not through, other side; open flat. Place plastic wrap over pork; pound to an even thickness using a meat mallet or rolling pin. Refrigerate until ready to use.
To prepare stuffing, cook rice according to package directions, omitting salt and fat. Add spinach and 1/2 teaspoon salt to hot rice, stirring until the spinach wilts. Stir in olives, red pepper, 1 teaspoon rind, and juice.
Spread rice mixture over pork, leaving a 1/2-inch border around outside edges. Roll up pork, jelly-roll fashion, starting with a long side. Secure both ends with twine; secure middle at 2-inch intervals with twine. Rub black pepper over pork. Place pork on a broiler pan. Bake at 325° for 1 hour and 20 minutes or until a thermometer registers 155°. Let pork stand 10 minutes before slicing.