Slice beef thinly. Chop off the right and left ends of onion, cut into half and slice each halved onion thinly. Mince garlic
Make sauce. In a bowl, mix together peanut butter, sriracha sauce and soy sauce.
Cut each halved Italian bread into half horizontally. Hollow out some of the soft white bread part from inside. Spread butter on each cut side of the bread and place breads on a baking sheet, butter side up, and bake in preheated 375 degrees F oven for about 5 minutes until slightly brown. Keep the breads warm.
In a skillet, heat olive oil and cook garlic and onion over medium heat until onions are tender. Add beef and cook until beef are cooked through. Add sauce to the skillet. Sauté the beef mixture to coat the sauce well. Add salt and black pepper to taste.
Put the beef mixture on the bottom of each bread (drip off the excess sauce), place cheeses (3 slices for each) and put the top of each bread to close sandwich.
Return the sandwiches to the oven and bake for 3-4 minutes until cheese melt.
Cut each sandwich into half and place on each serving plate.