Pour the whole can of chickpeas (garbanzo beans) and their water into a food processor along with all but one of the cooked beetroot. Blend until almost smooth.
Add the walnuts (keeping a small handful back), lemon juice and half the mint. Blend until the hummus reaches your desired consistency. I like it still with some texture, but this is up to you. Season to taste with salt and pepper.
To serve, transfer the beetroot and walnut hummus onto a large plate or into a bowl and top with more cubed beetroot, chopped walnuts and the rest of the fresh mint.