Step 1

Preheat oven to 350 degrees F (175 degrees C).

Step 2

Heat the vegetable oil in a skillet over medium heat. Add the onion, and cook until the onion has softened and turned translucent, about 5 minutes. Meanwhile, spread the baked beans in a casserole dish. Toss the corned beef with the tomato puree and Worcestershire sauce in a bowl and sprinkle over the beans. Spread the onions overtop, followed by the mashed potatoes. Finally, sprinkle with the shredded Cheddar cheese.

Step 3

Bake in preheated oven for 30 minutes until the casserole is hot and bubbly.