In a non-stick skillet over medium heat, brown the sausages in the oil for 6 to 8 minutes or until they are cooked through.
On a work surface, cut the baguettes horizontally without completely detaching the two parts. Brush the inside of each baguette with half of the harissa mayonnaise. Fill with the sausages and fries. Drizzle with the remaining mayonnaise.
Merguez are sold raw or pre-cooked. We chose raw sausages for this recipe and counted one hot dog per person (if you’ve got heartier eaters in your crowd, count two hot dogs per person).
Choose a soft-crust baguette for this sandwich; it will be much easier to eat. You can also serve the hot dogs in ciabatta buns with the fries and sauce on the side.