Dry rub: in a small bowl, combine salt, black pepper, onion powder, garlic powder, paprika, celery salt, and cayenne pepper powder. This is the dry rub for the roast pork.

Roast pork: preheat your oven to 350 F (175 C).

Cover the pork with a thin layer of Dijon mustard and then liberally sprinkle on the dry rub seasoning. I do this one side at a time. But make sure all sides of the pork are covered in mustard and dry rub.  

If you have a probe thermometer, insert it at the deepest part of the pork and bake until the internal temperature hits 145 F (63 C). This took me just under 2 hours. 

Allow the pork to rest for 1 hour, and then wrap it in plastic wrap and/or foil and place it in the fridge overnight. The next morning, slice the pork roast in thin slices and store the slices in the fridge until it is time to sandwich.

Bake bacon: line a sheet pan with aluminum foil. I typically overlap two or three pieces. 

Remove the bacon from the package and lay as many slices as you can on the foil-lined baking sheet. You can place your bacon very close together, but try not to overlap the pieces. If you can't get the whole package on there, put the remainder back in the fridge for later. 

Do not preheat your oven. When you have as much bacon as you can fit on your sheet pan, place it in a cold oven and set it to 400 degrees F (204 C). 

Set a timer for 20 minutes and start checking the bacon. Depending on the type of bacon and thickness, it could take another 5 or more minutes. 

I start checking at 20 minutes, and if it's not fully done, I will flip the bacon and put it back in the oven for another 5 minutes or so, checking the doneness every so often. Once the bacon is done to your liking, remove the slices to a paper towel-lined plate and store them in the fridge if you're not using them immediately. 

Reserve the bacon grease: carefully pour the liquid grease in the pan into a jar and allow to cool on the counter. This will be used in the hot bacon dressing.

Hot bacon dressing: in a small skillet over medium heat, add 2 tablespoons of the bacon grease. Once the grease has fully melted, add 1 clove of minced or pressed garlic. Saute for 1 minute, and then add the sugar, salt, and red wine vinegar. Cook the dressing for another 2 to 3 minutes or until everything is nice and hot, and remove the pan from the heat. 

Salad assembly: if your pieces of baby spinach seem large, you can chop them. This will help the salad to be in slightly smaller pieces on the sandwich. Add the spinach to a bowl with sliced and chopped red onion and chopped bacon pieces. 

Top the salad with some of the hot bacon dressing and toss. 

Sandwich assembly: slice your bread roll and add mayonnaise and/or mustard to the bottom of the roll. Top that with several slices of the roast pork and 2 to 3 slices of fresh mozzarella. Place both the bottom of the sandwich roll (covered with meat and cheese) and the top of the roll under the broiler for 4 to 5 minutes to toast the top roll and melt the mozzarella. If you do not have a broiler, you can preheat your oven to 350 F (175 C) and bake the sandwich pieces for 5 to 7 minutes or until the mozzarella is melty. 

Once the cheese is melty and the top of the roll is toasty, add the spinach salad on top of the mozzarella and close up the top of the roll to complete the sandwich. Wrap the sandwich in paper or foil to make serving a bit easier, and compress the sandwich ingredients just a bit more. Serve and enjoy.