In a small bowl, stir together mayonnaise, Italian seasoning, salt, and pepper. Spread mayonnaise mixture onto one side of each bread slice. Place cheese on mayonnaise side of 6 bread slices. Place roasted peppers on top of cheese, shingling to fit. Arrange ham slices and pepperoni slices on top of roasted peppers. Top with remaining 6 bread slices, mayonnaise side down.
Using a serrated bread knife in a gentle sawing motion, trim and discard crusts from sandwiches. Cut each sandwich into 2 (3×1-inch) finger sandwiches. Cover with damp paper towels, place in an airtight container, and refrigerate until ready to serve.
Garnish with rosemary sprigs, if desired.
Recipe by TeaTime Magazine at https://teatimemagazine.com/ham-pepperoni-and-cheddar-tea-sandwiches/