Preheat Blackstone griddle to medium heat. In a medium mixing bowl, combine the shrimp, cornstarch, and 1 tablespoon Cajun seasoning. Toss until the shrimp are fully coated.
Drizzle vegetable oil over the griddle top then add the shrimp. Cook for 4 minutes per side. The shrimp should be very crispy. Once cooked, remove from griddle and set onto a paper towel-lined plate.
Toast the French bread and then set aside. Whisk together the mayonnaise and remaining Cajun seasoning in a small bowl.
Build the sandwiches by layering the spicy mayo, shrimp, shredded lettuce, and tomatoes evenly onto the French bread. Serve immediately.
