1. Put potato slices and water in a shallow glass dish; cover with plastic wrap.
2. Microwave on HIGH for 10 minutes or until tender; stir once after 5 minutes; drain and set aside.
3. In a large saucepan, melt 2 tablespoons butter over med-high heat.
4. Add in the onion; saute/stir for 5 minutes or until tender.
5. Add potato slices; toss gently; transfer mixture to another container and set aside.
6. Melt remaining 2 tablespoons butter in saucepan over med heat.
7. Gradually whisk in milk and gravy mix; whisk until texture is smooth.
8. Add in the shredded cheese; whisk until cheese is melted.
9. Remove saucepan from heat; add potato mixture; stir to combine.
10. Spoon mixture into a lightly greased 9-inch square baking dish.
11. Combine the breadcrumbs and parsley; sprinkle evenly over the potatoes.
12. Bake at 400° for 25-30 minutes or until bubbly.