Brush the mussels thoroughly under cold running water and drain well. Discard open mussels. Peel and chop the garlic. Wash the pepperoni. Wash and cut tomatoes into eighths. For the spaghetti, boil 3-4 l salted water (approx. 1 teaspoon salt per litre).
Heat the oil in a large pan with a lid. Sauté the garlic and pepperoni briefly. Season with salt and pepper. Add the mussels, heat and cook covered for 4-6 minutes, tossing the pan from time to time.
Throw away closed shells. Fold in tomatoes and heat briefly. Season to taste with salt and pepper.
Meanwhile, pour the spaghetti into boiling salted water and cook until firm to the bite according to the instructions on the packet. Wash parsley, shake dry and chop finely. Pour the pasta into a sieve, drain and put it back into the pot.
Fold in mussels and parsley. Arrange everything.