To cook the bacon, set the stove to 400 degrees Fahrenheit. Lay parchment paper on a baking sheet and add the raw bacon on the sheet lined up next to each other. Cook for about 20 minutes or until the bacon has reached your desired amount of crispness. Once cooked, set the bacon on a plate covered with paper towels to soak up the excess grease. Set aside.

Peel and slice the onion. Slice the tomatoes. 

Heat a skillet on the stovetop over medium heat. Add two tablespoons of butter or olive oil. Add the onion to the skillet, combining it with the butter/oil in the skillet. Using a metal tong separate the onion slices from each other and cook until the onion is translucent and a little golden brown, or about 5-7 minutes.

Remove the onions from the skillet onto a plate while you assemble the grilled cheese.

Butter the outside of all slices of bread. Flip the bread over and add the Cheddar, Provolone, and Swiss cheese to both sides of each sandwich bread. It's up to your discretion whether you want to split each slice of cheese in half or add a full slice. 

Add the bacon slices, tomatoes, and fried onions. Before closing the sandwich together, add an extra slice or two of cheese if you wish. 

Place the sandwiches butter side down on the skillet and cook for about 2-3 minutes on each side, or until golden brown. 

Pair with tomato soup or a salad of your choice! Enjoy.