Preheat your griddle to medium. Use kitchen scissors to cut the bacon right onto the griddle. Cook 7 to 9 minutes, mixing a few times and scoot the bacon to side of griddle. Scrape some of the bacon grease into the grease trap.
Add the onions and mushrooms to griddle, cook 5 minutes mixing with spatulas. Add the green beans, garlic, kosher salt, pepper, and seasoning blend of choice. Cook 5 minutes, mixing with spatulas.
Add the bacon to the green bean mixture and mix together for a minute. Scoot everything to side of griddle and scrape center of griddle clean. Place a foil 9x13 pan in center of griddle and transfer everything to the foil pan.
Add the heavy cream and 6 ounces of the parmesan cheese. Stir, lower griddle heat, and let it bubble on the griddle for about 5 to 10 minutes, stirring a few times.
Toss the bread cubes with the melted butter, remaining parmesan cheese, kosher salt, pepper, and seasoning blend of choice. Add this to the green bean casserole, pressing it into the casserole slightly.
Transfer this to either the oven or pellet grill set to 350 degrees for 35 to 45 minutes.