In a large skillet, add the oil on medium-low heat. When hot, add garlic and sauté a minute.
Add the bell pepper and cook covered until softened.
Add the tomato puree, tomato paste, harissa, spices and cook for about 3 minutes. Add a little warm water if too thick.
While the sauce is cooking, grill the Merguez sausages until fully cooked.
When ready, cut the Merguez in half, transfer to the sauce and warm for a few minutes.