Preheat oven to 350 degrees and spray 9x13 pan with cooking spray
Cook lasagna noodles per package directions and drain- set aside
Heat large skillet and add 1 stick of butter and all diced onions and salt.
Add onions to mashed potatoes and cheddar cheese mixture. Add pepper and mix well
Place 3 cooked noodles on bottom of pan. Spread ⅓ of potato cheese mixture over noodles. Repeat layers until top layer of noodles and then add the ½ moon onions
Cover with aluminum foil and bake for 25-30 minutes.
