Prepare the celery by removing its strings, cutting it lengthwise, and slicing thinly at an angle. Halve the cherry tomatoes and mince the garlic.

Toast breadcrumbs in a frying pan over medium heat until golden brown. Transfer to a bowl, let cool, then mix with Parmesan cheese and dried parsley.

Boil water in a pot and cook spaghetti according to package instructions. Reserve 100ml of pasta water.

Heat olive oil, garlic, and chili flakes in a frying pan over medium heat. Once fragrant, add celery and sauté until translucent. Add the canned mackerel with its liquid and cook for 2 minutes, breaking it apart.