1. Heat oil in a saucepan (not more than half full) over medium-high heat to 365 degrees on a deep-fat fry thermometer. Adjust temperature under pot to maintain 365 degrees .
2. In a large bowl, whisk together the bread crumbs, Cajun seasoning and salt. Heat oven to 200 degrees . Line a large baking sheet with a double layer of paper towels.
3. Toss 1/3 of the shrimp with egg whites. With tongs or a slotted spoon, transfer shrimp to bread crumb mixture and toss to coat. Fry in 365 degrees oil for 2 minutes. Remove with a slotted spoon to papertowel- lined sheet and keep warm in 200 degrees oven. Repeat twice more with remaining shrimp, egg whites and bread crumb mixture (you will have egg white and bread crumbs leftover).
4. Fry shrimp in 2 more batches, letting oil return to 360 degrees to 365 degrees before adding next batch.
5. Meanwhile, spread 1 tbsp tartar sauce on each hoagie roll or Italian bread section. Top each with 1/4 cup arugula leaves, about 8 shrimp and 2 tomato slices. Sandwich and serve.