Bake tots on a rimmed sheet at 425°F for 20–25 minutes until golden and crisp. Toss once halfway.
Meanwhile heat oil in a large skillet over medium. Add onion and pepper; cook 5 minutes until soft.
Add chopped corned beef, garlic powder, salt, and pepper. Cook 6–8 minutes until edges brown.
Spread baked tots in a large baking dish. Spoon corned beef hash over tots and press lightly.
Poach eggs: bring 3 quarts water and vinegar to a simmer, stir to create whirlpool, crack eggs one at a time and cook 3 minutes for runny yolks.
Top casserole with poached eggs and parsley. Serve immediately.