Peel and coarsely chop the carrot. Bring a pot of salted water to a boil. Add the carrots, reduce the heat to low, cover and simmer until soft, about 10 minutes. Drain well. Finely chop the olives. Rinse the scallions and put some green aside for garnish; finely chop the rest and place in a bowl with the olives. Puree the carrots in a blender. Add the olive mixture, the harissa and lemon juice, and mix briefly. Season with salt.
Roast the sesame seeds with sea salt in a dry skillet, stirring 1-2 minutes until golden. Crush the sesame seeds in a mortar or spice mill. Spread the carrot mixture on slices of bread and sprinkle with sesame salt. Serve garnished with scallion greens.