Preheat oven to 400F.
Mix up some sriracha and mayo to your preferred level of spicy and set aside.
Lay your bread out on a baking sheet (tops and bottoms) and spread pesto paste on the bottom of the bread.
Add chicken, spinach, tomato, onion and provolone cheese.
Bake for about 5 minutes (tops off) until cheese is melted.
Remove from oven and carefully dress the top bun with the spicy mayo. Place the top bun on top of the sandwich, then return to the oven for another 5 minutes or until the bread begins to brown lightly on top.
Remove from oven and serve hot! Enjoy!