Preheat oven to 375°F. Spray a 9x13 baking dish with nonstick cooking spray and set aside.
Heat a large skillet over medium-high heat. Add bacon and cook until crispy. Remove with a slotted spoon and place on a paper-lined plate. Drain all but 2 tablespoon of the bacon grease. Add the shallots and cook for 4-5 minutes, or until translucent. Add the garlic and cook for another 30 seconds. Remove from heat and set aside.
In a large bowl, add the mashed potatoes, shallots, garlic, half of the bacon and 1 cup of cheese. Mix until combined. Season with salt and pepper if needed.
Lay 3 cooked lasagna noodles on the bottom of the dish. Add ⅓ of the potato mixture followed by 1 cup of cheese. Repeat 2 more times, finishing with the cheese. Cover with foil and bake for 30 minutes. Remove the foil, sprinkle on the remaining bacon and green onions and bake for another 5 minutes. Allow to cool for 15 minutes before slicing.
Notes
If you like tart, tangy flavor in your potatoes, stir in ½ to 1 cup of sour cream in the mashed potato mixture.
Don’t use pre-shredded cheese. It doesn’t taste as good and also has additional ingredients that you don’t need.
If you want to save a few minutes, no boil lasagna noodles can be used.
You can prepare the lasagna a day ahead of time. Just cover in the fridge before placing in oven to cook. You will have to cook 5-10 minutes longer.