Trim off excessive fat.
Place pork on work surface with fat side up. Cut horizontally across 1/3 up above bottom to within 1/2“ of far side. Open meat and cut thick side in half to within 1/2” of far side. Unroll meat and lay flat. Place plastic wrap over pork, pound to an even thickness using a meat mallet or heavy object. Refrigerate until ready to use.
In large saucepan (3 qut.) with space to add rice, cook rice according to package directions, omitting salt and fat. Add spinach and 1/2 tsp salt to hot rice, stirring until the spinach wilts. Stir in olives, red pepper, lemon rind, and juice.
Spread rice mixture over pork leaving a 1/2“ border around outside edges. Roll up pork, jelly-roll fashion, starting with a long side. Secure both ends with twine, secure center section at 2” intervals with twine. Rub black pepper over pork. Place in oven to cook or refrigerate up to 2 days for later cooking.