Preheat the oven to 400. Cover a rimmed baking sheet with parchment paper and set aside.
In a small bowl, mix the tomato paste, onion powder, garlic powder, Italian seasoning and salt and stir to combine. Set aside.
Lightly flour your work surface and unfold the puff pastry, removing the paper between. Using a rolling pin or glass, lightly roll the pastry until it's 1 inch larger on all sides and slightly thinner.
Using a knife, follow the fold lines in the pastry to cut three long strips. Cut the strips in half to make 6 rectangles. One row will be the hot pocket bottoms and one row will be the tops.
Spread 1 teaspoon (or a little less) of the tomato paste mixture in to the center of the three bottom rectangles, leaving a 1/2 inch border.
Add 2 tablespoons of cheese to each one, then top each one with three or four pepperoni.
In a small bowl beat together the egg and water. Using a pastry brush or your fingers, brush around the border of the bottom piece and then lay the top piece on. Use your fingers to press the edges together well.
Transfer the first three to your baking sheet and repeat with the second sheet of puff pastry.
Using a knife, poke three holes in the top of each hot pocket to let out steam. Brush with egg and sprinkle evenly with Italian seasoning and parmesan cheese if desired.
Bake until puffed and golden, about 15 to 20 minutes. Allow to cool 5 minutes before eating.
To save for later: cool to room temperature and transfer the hot pockets to a zip lock bag or air tight container. Store in the refrigerator for up to a week. Microwave 30-45 seconds before enjoying.