In a mixing bowl, combine the cream cheese, shredded cheddar cheese, chopped jalapeños, mozzarella cheese, garlic powder, onion powder, salt, and pepper. Mix until well combined. This will be your spicy cheese filling.
Spread about 2 tablespoons of the butter on one side of each slice of bread. These will be the outside of the sandwiches.
Lay 4 slices of the bread, butter side down, in the frying pan over medium heat.
Divide the cheese mixture evenly among the 4 slices of bread in the pan. Top with the remaining 4 slices of bread, butter side up, to form sandwiches.
Cook for about 3-4 minutes until the bottom is golden brown. Carefully flip the sandwiches using a spatula.
Cook for another 3-4 minutes, pressing down lightly with the spatula, until the other side is golden and the cheese is melted.
Remove from the pan and let them rest for a minute before slicing.