Do you also have trouble getting some foods sliced and diced evenly and consistently? Here's a quick print that can help!

The “Slice" file is the main file to use, but the “Dice” print is meant to fit over the top of the “Slice” print so you can use them together. 

I recommend printing in PETG or similar filament to make sure it is foodsafe. This is a functional work-in-progress. I saw a similar product made of metal, and figured I could make something similar. I've tested this on an onion, and it works, but you likely won't be able get it to pierce all the way through - but you don't need to. Even the prongs that don't contact the food to be sliced still help as a guide.

The prongs are generally long enough to penetrate far into your food-item and still give clearance for a knife, but only just. Making them much longer makes them too flexible and you'll get less consistent cuts. Even still, in PETG those extra-long prongs are strong enough to not break. 

Please, give suggestions on how to improve this idea!

This was tested on an onion and it works, but don't expect the prongs to go all the way through. If you push too hard, the ones on any edges won't bite into the food, but will bend out to the side if the angle is too steep.