Fry bacon, drain and chop or crumble into small pieces. Chop green onions and set it and the bacon aside in refrigerator until ready to use.
Bring 8 1/2 cups of water to boil with 1 tablespoon salt. Peel and chop potatoes. Add to boiling water. Reduce heat to medium high and boil potatoes for 20 minutes or until very tender. Strain potatoes. I recommend using a potato ricer for this recipe (any mashed potato recipe), but if you do not have access to one then a masher or mixer will work.
Preheat oven for 350 degrees F. If warming on the grill, set over medium-high to medium indirect heat for 20-25 minutes.
In a medium microwave safe bowl melt butter. Add melted butter to pot with evaporated milk, 3/4 of the chopped green onion, 3/4 of the chopped bacon, 1 cup of the cheese, garlic, 1 teaspoon salt, and black pepper. Stir to combine. Taste for salt content and add the remaining 1 teaspoon salt if needed.
Scoop potato mixture into a casserole pan or disposable aluminum pan (if grilling), and top with remaining, cheese, green onion, and bacon. Bake for 20-25 minutes, or until cheese has melted and sides are beginning to brown.
Remove from oven (or grill), and serve.
Store leftovers in an air tight container in refrigerator for up 4 or 5 days after initial preparation.