Preheat the oven to 220°C.
Rub the skin of beetroot using the rough side of a new washing-up sponge and cut off the roots (but do not peel).
In a bowl, mix the oil with the juice of 1 lemon. Sprinkle the rosemary leaves and garlic on top, then season with salt and pepper.
Add the beetroot (whole), cover with the marinade, then put them in a roasting pan. Pour over any leftover marinade.
Bake in the oven until tender, for about 30- 40 minutes, turning over a couple of times.
Cook the lentils in boiling water until tender, then drain.
Steam the broccoli over the lentils in a bamboo basket (or cook in another saucepan) for a few minutes.
Add the broccoli to the beets for the last 10 minutes of baking, basted with the juices.
Transfer the roasted vegetables and juices to a serving dish. Cut the beets into wedges then add the lentils and toss well.
Drizzle with some olive oil and lemon juice. Season with salt to taste and pepper. Serve it warm or at room temperature.