Place the sub roll on a board and slice it lengthwise using a serrated knife, keeping one side attached so it opens like a hinge. Remove a small amount of the soft center if needed to create space for fillings.

Spread mayonnaise evenly on both inner sides of the bread, making sure to reach the edges. Drizzle olive oil lightly over the surface, followed by a few drops of vinegar. Let it absorb slightly into the bread.

Arrange the beef salami slices on the bottom half, folding each slice gently to create layers. Add the turkey or chicken slices on top, spreading them out evenly.

Place provolone cheese slices over the meat, slightly overlapping them so the surface is well covered.

Add shredded lettuce evenly, followed by tomato slices placed in a single layer. Top with thin onion slices spread across the sandwich.

Sprinkle salt, pepper, and dried oregano evenly over the vegetables to enhance the flavor.

Close the sandwich carefully and press down gently with your hands to hold everything together. Let it rest for a few minutes so the flavors blend.

Cut the sandwich into halves using a sharp knife and serve immediately.