Final answer:
The preparation of pre-cooked, sliced, and fried vegetables with onions is known as 'hashing.' It often refers to potatoes and results in a dish commonly called 'hash browns.'
Step-by-step explanation:
The term that describes vegetables that are pre-cooked, sliced, and fried with onions, a classic potato preparation, is c) Hashing. Hashing refers to chopping food into small pieces and then cooking it, often with onions and other seasoning. When applied to potatoes, it's commonly known as "hash browns" or simply "hash," a dish where the potatoes are diced, blanched or parboiled, then fried with onions to create a crispy texture on the outside while remaining soft and cooked on the inside.