Slice the buns in half horizontally. Place the buns on a baking sheet. Slather each half of the buns with some marinara sauce. Top each side with mozzarella cheese. Top the bottom half of each bun with lots of pepperoni slices. Bake in the oven for 8-10 minutes.
In the meantime, toss together the romaine lettuce with as much caesar dressing as you like. Stir in the parmesan cheese and lemon juice. Season with black pepper to taste. Toss in the seasoned croutons.
Remove the pizza buns from the oven, let cool slightly. Place some of the salad mixture on top of the pepperoni side of the buns. Close up each sandwich with the top of the bun.