Preheat the oven to 190°C. Line a shallow roasting tray with baking paper.
Cut the carrots in half lengthwise and place in the roasting tray. Pour over 2 tablespoons olive oil and season with salt and freshly ground black pepper. Toss well to coat in oil then spread out in a single layer. Place in the oven and roast until tender and golden, about 20 minutes or so.
Meanwhile, place the lentils in a saucepan with plenty of cold water. Bring to the boil, reduce to a simmer and cook for 20 minutes or until just tender. Drain.
Steam the fresh green beans until tender.
In a large bowl, whisk together the Dijon mustard, vinegar and shallot. Season, then whisk in the remaining 4 tablespoons olive oil. Add the well-drained green lentils and the fresh green beans and toss.
Remove carrots from the oven and top with the lentils, green beans and all the dressing. Dollop with sour cream and scatter over the coriander leaves and seeds mix, if using and serve.