I use a cheap mini food processor for small tasks such as this - ones where my full-size gear would just be too big & I'd either lose most of it round the edges or it would just go underneath the blades & I'd spend all my time bouncing it up & down trying to get it to work on such a small quantity.

Small batches, but you only need to rough chop, so time is saved overall.

Asda, 8 quid [ten bucks or so] No clue what make it is. Plenty powerful for its size.  
Hand-held so you can estimate its size. 

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  [1]: https://i.sstatic.net/703sC.jpg