Do you mean skewering tomatoes is your job? As in, you work in a kitchen and make shish kebabs? You could say "I make shish kebabs for a living." or "My job is to skewer small tomatoes together." The latter still sounds a bit strange just because you do more at work than that, right? Here "skewer" can be used as a verb instead of "hold" because you are using a skewer. What's unclear is: your role in what? So if in context of a conversation it's clear you're talking about your role in something in particular, like "my role [at the restaurant]" then it would make sense but without context it's unclear what you mean by your "role." What you have written could be a response to a question, "and what is your role at the restaurant?" or "how do you help your mother make shish kebabs at home?" In the second case "my role [in helping my mother cook]..." would be understood. Grammatically, it already makes sense, just use the plural for tomatoes. In English, words that end in O often get the -es plural ending.