Can I slice tomatoes on the Sabbath for eating?
Thank you for your question.
It is permitted to slice tomatoes on the Sabbath.
While there is an issue with cutting vegetables into small pieces, even if they were sliced very thin, it is still permitted. According to many Poskim, food that is sliced in long, thin strips. Although the thin side is indeed thin, since it is not small along the length it is not considered tochain, and may be done on Shabbos. In contrast to this, breaking a splinter off a piece of wood to use as a toothpick is not permitted. This is because this is the desired size needed. Regarding the tomato, although you do want the specific size that you cut it, it is not unusable if it will be a little bigger. Regarding the splinter, if it is bigger it isn’t useable as a toothpick.
Have a good Shabbos
Igros Moshe O:CH 4 74 Tochain 3, Shvisas Hashabbos Tochain 7, Minchas Shlomo 91-13, Shmiras Shabbos K’hilchoso ( old edition) 6-10, Nishmas Shabbos 315.