I'm aiming to get my 5-aday, and wondered if onions had any nutrional value to them?

Onions are good for you as part of a balanced diet. Bad for the breath... but good for the body. Yes they have a nutritional value. Few negatives.

Yeah, onions have some nutritional value to them. Here's a good serving size guide for veggies and fruits. Serving Sizes for Fruits and Vegetables

According to that 4 slices of an onion= 1 serving.