In 10-inch saute pan, heat 2 tablespoons olive oil over medium heat; saute onion 3 minutes, or until translucent. Stir in broccoli rabe and red pepper flakes; cover and cook over medium heat 2-3 minutes, or until broccoli rabe is wilted. Sprinkle with 1/4 teaspoon salt and pepper, to taste; stir in olives, if desired. Transfer mixture to bowl; cover and keep warm.
In small paper or plastic bag, combine flour and remaining salt. One at a time, add chicken cutlets; shake to coat each cutlet in flour then transfer to plate. Dip cutlets in egg then bread crumbs and return to plate. Set aside.
In skillet over medium-high heat, heat remaining olive oil. Working in batches, brown chicken, cooking 2-3 minutes, or until golden on each side and no longer pink inside.
To serve: Top each bread slice with one chicken cutlet; spread with broccoli rabe mixture. Top with slices of provolone, if desired. Top with remaining bread.