Scrub each mussel individually, trying to remove as many of the stringy pieces that cling to the outside as possible. Then, look at the crack where the two shells meet on the mussel and pinch the strands that look like threads of brown seaweed, tugging to remove. Repeat with all mussels and set aside.

Heat the olive oil over medium heat in a large non-stick skillet. Once oil heats, crumble in the sausage and cook until browned, about 5 minutes. Then, add in the celery, onion, red pepper flakes and garlic and cook until vegetables soften, 3-5 minutes.

Raise the heat to medium-high and add in the tomatoes, season with salt and pepper and cover, cooking another 5 minutes.

Lower the heat and add in the basil and mussels. Cover the pan again and cook until the mussels open, about 2 minutes. Discard any that do not open.

Add the zucchini noodles into a large serving bowl and then pour over the mussel mixture and toss to combine. As the sauce sits over the noodles, it will soften them. Let sit for 2 minutes for the flavors to absorb and then serve.