Preheat oven to 180°C. Cut beetroot into bite sized pieces. Lay on a baking tray and drizzle with olive oil. Bake in oven for 30 minutes until tender. Allow to cool.
Arrange the spinach leaves on four serving plates. Top with pieces of beetroot, mandarin segments and crumble over the feta cheese.
To make the dressing, mix all the ingredients together in a glass jar, give it a good shake. Drizzle Marmite™ dressing over the salad and garnish with basil leaves.