Peel and finely chop the onion. Peel the carrots and turnips, then cut them into cubes. Remove the strings from the celery and finely chop it. Wash the zucchinis and cut them into thick slices, then quarter the slices. Place the raisins in a bowl of hot tea.
Heat a large pot and brown the merguez sausages over medium heat without adding any fat. Remove the sausages and add the onion, celery, and ras el-hanout. Season with salt. Let them sweat for 3 minutes. Then, pour in the vegetable broth and bring to a boil.
Add the carrots, turnips, chickpeas, and zucchinis to the broth and cook covered on low heat for 45 minutes. Adjust the seasoning.
Meanwhile, prepare the couscous according to the package instructions.
Reheat the merguez sausages and drain the raisins, squeezing them gently. Arrange the plates with couscous, merguez sausages, vegetables, and raisins. Garnish with chervil and serve with the broth on the side (and harissa if you like).