Bake the sweet potato fries as the label directs; season with salt and 1/4 teaspoon ras el hanout. Reduce the oven temperature to 250 degrees F and keep the fries warm in the oven. Meanwhile, mix the mayonnaise, harissa and 1 grated garlic clove in a small bowl; refrigerate until ready to use.
Combine the ground beef, parsley and the remaining 2 grated garlic cloves and 11/2 teaspoons ras el hanout in a large bowl. Mix with your hands until just combined. Form into four 3/4-inch-thick patties; season on both sides with salt and pepper. Heat the vegetable oil in a large nonstick skillet over medium-high heat. Add the burgers and cook until browned, 3 to 5 minutes per side for medium rare.
Serve the burgers on the buns with a spoonful of the harissa mayonnaise and some sliced tomatoes, arugula and olives. Serve with the sweet potato fries and remaining harissa mayonnaise.