io. What are 'pinches' as in "4 pinches sweet potato" and ".5 pinches onion"?

Looking at the recipe, it appears to be a typo for "pieces". Some recipe generators have a drop down menu to select the unit of measure, so the author could have accidentally selected the wrong word. I would interpret this as 4 Sweet Potatoes, half of an onion.

A pinch is generally referring to spices and seasonings in amounts too small to measure: use your personal taste as a guide. A "pinch" because ti is an amount you can pinch between too fingers. In your example, it is just poor recipe writing.