Drain the tuna from the oil
Wash and slice the radishes.
Clean and wash the salad and dry it thoroughly.
Prepare the sauce by emulsifying together the oil, lemon juice (I suggest you add a little at a time), and mustard. Season with salt if necessary.
Arrange the salad in a large bowl, add the radishes and the chopped tuna. Pour in the desired seasoning and mix well.
Finally, add the blackberries and chopped walnuts.