If you are having a barbecue in the south-west of WA, you can save yourself some tears, quite literally, by ordering bulk chopped onions from the local prison.

Bunbury Regional Prison not only grows its own vegetables and supplies six other regional prisons in the state, it also takes orders from the public for bulk chopped vegetables.

The prisoners do the chopping and the most in-demand vegetable is the onion.

The vocational support officer for vegetable preparation Barry Conway said that the onions for many charity or volunteer barbecues in the city have most likely come from the prison.

"They all just get their onions for the weekend sausage sizzles."

The Bunbury prison cuts onions to order. ( ABC South West: Katrina Beavan )

Despite chopping on average one to two tonnes of onions per week, Mr Conway said the prisoners managed to contain their tears by using safety glasses and good ventilation.

"I haven't seen any of them cry yet. What happens, if they can feel the build up there, they just walk outside ... I think some of the other prison officers struggle when they walk through here."

Community groups use the prison service because they can buy in bulk, Mr Conway said.

"I wouldn't want to peel 20 kilograms of onions myself and chop them up."

The process starts with pallets of whole onions in bags.

The prisoners enjoy the change in routine. ( ABC South West: Katrina Beavan )

One prisoner who has been chopping onions for eight months explained that firstly the vegetables were topped and tailed with a knife.

"We use the compressor and blow the skins off, give them a wash and chuck them in the cool room."

The onions were then chopped in a machine, bagged by the prisoners and sealed in air tight bags ready for pick up.

The same person, who cannot be named, said that he valued the program.

"It makes the day go heaps quicker; it gives us something to do instead of sitting around thinking about things," he said.

Prisoners learn numeracy and literacy skills

If the prisoners are not put to work prepping vegetables, they repair old trailers or make furniture to also sell.

Prison business manager Roz Marocchi explained that about 100 prisoners were employed in the facility.

"All the prisoners in here undergo training ... They'll have a qualification they didn't have when they first came in."

She said the programs function much like a working day.

"They have to get up every morning. They have to come to work. They have to stay at work all day and then at the end of the week they get their small gratuity payment," she said.

"Most of these prisoners have very low numeracy and literacy skills.

"This teaches them that they can learn. It encourages them to engage with education."