Shorten the stems of the beet tubers a little bit. Cook the tubers in enough boiling salted water for 45 minutes until al dente. Drain the beet, rinse when cool and remove the skin. Cut tubers into wedges and cool.
Stir orange juice, fruit vinegar and olive oil in a baking bowl to make a marinade. Squeeze garlic clove through a press and season well with salt and freshly ground pepper. Drizzle four tablespoons marinade over beet wedges (for 4 servings) and toss to coat.
Clean and rinse the spring onions and cut into fine rings. Fold onion rings into remaining marinade. Peel oranges so that the white skin is completely removed. Carefully remove the orange fillets between the separating skins. Toast flaked almonds in a dry frying pan without fat until golden brown and set aside.
Place the beet wedges in a sieve, drain well and arrange on plates with the orange fillets. Spread the spring onions with the marinade evenly over the beet as well as the oranges. Sprinkle everything with the toasted almond flakes.