If you find a raw red onion a bit strong, you can microwave it for a couple of minutes, or soak in boiling water for a couple of mins.
Combine all of the ingredients (except the bread) in a bowl and mix gently together. Season to taste with salt and pepper.
Serve on a slice of toast.
Notes
Prep Tips:With the addition of the lemon juice, this will store until the next day in an air tight container in the fridge. Health Tips:Choosing tuna in spring water can reduce the amount of salt in our food. Don't peel your apple for this, the skin contains a lot of the nutrients and the fibre so will slow down your digestion of the sugars (and help your food move through your bowels). Eco Tips:You should be able to get all the veg out of packaging. Make sure your tuna is from a sustainable source that at least has the MSC certification. Ideally it should state how the tuna is caught or be 'dolphin-friendly' as the trawler nets used sometimes capture huge amounts of other species.