Zucchini, unlike broccoli and onions, does not cause gas. Some vegetables, especially cabbage, broccoli, onions, cauliflower and peas, can cause flatulence. Experiencing gas is not only embarrassing for you, but it also indicates the presence of a deeper problem at the level of your gut flora. Imbalanced gut flora can excessively ferment certain types of carbohydrates found in some vegetables, as well as in some sugar, fruits, legumes and grains.