Cook lasagna noodles according to package directions. Drain, pat dry and interleave in a damp towel to keep moist OR spray each noodle with cooking spray OR lightly apply some oil.
In a separate large skillet over medium heat, combine the onions with the butter and saute for 5 minutes.
Prepare the instant mashed potatoes according to package directions, but omit the milk. Stir in the cream cheese until well blended.
Place 3 noodles in the bottom of a lightly greased 9x13-inch baking dish. Spread 1/2 the potato mixture over the noodles in the dish. Top this with 3 more noodles, followed by the other 1/2 of the potato mixture. Finish by topping with the remaining 3 noodles, then top those with sauteed onions.
Bake at 350 degrees F (175 degrees C) for 20 minutes, or until bubbly. Allow to cool for 5 minutes before cutting.