Boil the beetroots for 40–60 minutes or bake them for 60–90 minutes. Cool, peel, and slice very thinly.
Crush or finely chop the garlic. Mix it with olive oil, lemon juice, basil, salt, and pepper.
Place the beet slices in a bowl, add the marinade, and gently mix. Let marinate for at least 2 hours or overnight.
Serve on a plate with arugula, cheese, and sprinkle with nuts (toast them if desired).