Cook pasta according to package description.
Roast the walnuts in a large dry pan on medium heat for a couple of minutes.
Dice the onion and garlic.
Put the walnuts into a small side bowl and add the onion and garlic to the pan with olive oil on low to medium heat. After 2 minutes season with sage, salt and pepper.
Open the packaged beetroot and pour the excess liquid into the pan. It should just be a few drops. Cut beetroot into small cubes and add it too.
Add the white wine vinegar to the mix.
Once ready, drain the pasta with a colander and collect about half a cup (100 ml) of the excess pasta water.
Add both the pasta and water to the pan.
Now it’s time for the coloring, if you bought the beet juice. Add it to the mix. Give everything a good stir and let it simmer for about 6 minutes and make the taste test.
While it’s simmering, wash and roughly cut the arugula.
Garnish with the arugula, feta, walnuts and lemon slices.