There are many vegetables that can help your Crohn's and keep your diet going, but there are also many vegetables that can make everything much worse. There are even some vegetables dieticians recommend to avoid during flare ups and then the complete opposite when feeling ok again.
Always avoid high acidity vegetables. Garlic and onions are an absolute no and try and avoid anything high fibre when you're feeling unwell. Peppers and courgettes can be a great go-to vegetable in your meals at almost any time.