Heat the olive oil in a heavy saucepan over a medium heat. Add the carrots, celery, onion and fennel. Reduce the heat to low and gently cook the vegetables, with the pan covered, for 10–15 minutes until they are all softened but not browned.
Add the tomatoes to the pan with the beetroot and cook for about 3 minutes longer. Stir in the orange zest with the stock. Bring the mixture to the boil, stirring occasionally, then cover the pan, reduce the heat and simmer for about 25 minutes until all the vegetables are tender.
Meanwhile, prepare the salsa and bagels. For the salsa, simply combine the ingredients together in a bowl. Then, for the bagel topping, blend the cream cheese with the horseradish sauce until well mixed. Toast the bagels, then spread the cheese mixture over the toasted bagel halves.
Remove the soup from the heat, blend in a blender or food processor until completely smooth, then return to the pan. Alternatively, blend the soup in the pan using a hand-held blender. Stir in the orange juice, and a little extra stock if too thick, then reheat gently and season to taste.
Serve the soup topped with a little of the beetroot salsa and accompanied by the bagels.