Heat olive oil in a medium-sized skillet, or griddle over medium-high heat. Add in onions and 2 tablespoons sriracha. Saute onions until soften and translucent, about 5 to 7 minutes. Remove onions from pan and set aside. (Optional): toast jalapeno slices for 1 to 2 minutes.
In a small bowl, mix together butter and remaining 1 tablespoon sriracha. Butter both sides of all 8 pieces of bread. Grill bread on a griddle over medium heat until 1 side of each piece is browned and toasted.
Assemble the sandwiches with the one toasted side up, on the inside of the sandwich. Assemble with 1 slice of pepper jack, some of the sriracha onions, another slice of pepper jack cheese, jalapeno slices and crumbled jalapeno chips, topped with a final slice of pepper jack cheese. Place the top piece of bread with the toasted side down.
Grill until the outside pieces of bread are toasted and the cheese is melted, flipping halfway through.