In a hot pan, cook the merguez pieces without any oil for 7–10 minutes, until browned. Remove from the pan and set aside, then discard the excess oil left behind.
Add the onion and tomato paste to the same pan and cook until the onion turns translucent.
Mix in the diced tomato, bell pepper, garlic, and spices, and cook until the tomatoes soften.
Add the water, tomato & basil sauce, harissa, and the merguez back into the pan. Stir to combine, cover, and simmer on medium-low heat for 20 minutes.
Boil the linguine according to the package instructions, then fold it into the sauce and serve.