Butter one side of each piece of bread. Place it butter side down into the pan. Top with one cheese, then the roasted red peppers, then the avocado, then the bacon (if you are using), then the arugula and then the other cheese. Place the second piece of bread, butter side up on top.
Flip when bread is golden brown and then grill the other side until golden brown and cheese is melted.
This is absolutely a perfectly, hearty, delicious meal. Everyone loves a good grilled cheese!