1. Bake tater tots according to the package.
2. In a large skillet, saute onions in oil until soft - about 5 minute.
3. Add hamburger to onions and brown.
4. Stir in cream of mushroom soup and green beans.
5. Pour mixture into a 9 x 13 pan, and arrange tater tots on top.
6. Sprinkle the cheese on top of the tater tots.
7. Bake at 350 degrees for 30 min or until cheese is browned.