Preheat the oven to 400 degrees F. Place a baking sheet in the oven to heat.
Toss the celery, sweet potatoes and red onions with the olive oil, ras el hanout and rosemary in a mixing bowl. Season with salt and pepper. Transfer the mixture to the heated baking sheet and roast until the potatoes are tender and caramelized, about 30 minutes.
Let the sweet potato mixture cool to room temperature before proceeding. (Or, if preparing ahead of time, cool the sweet potato mixture in the fridge, removing it 30 minutes before proceeding to allow it to come to room temperature.)
Toss the sweet potato mixture in a large bowl with the grapes, pecans, pomegranate seeds, scallions and raisins. Toss the salad with sherry vinegar and olive oil to taste. Add salt and pepper as needed.