Roughly chop the stale bread to create rustic breadcrumbs, then place in a large non-stick frying pan on a medium-high heat with 1 tablespoon of olive oil. Cook for 3 minutes, or until crispy, stirring regularly, then tip into a bowl for later. Trim the tough end off the broccoli stalk. Cut the florets into small, delicate pieces and very finely slice the remaining stalk. Peel and finely slice the garlic. Finely grate the lemon zest and put aside for later. Cook the pasta in a pan of salted boiling water according to the packet instructions, adding the broccoli florets for the final 2 minutes, then drain, reserving a mugful of the starchy cooking water. Meanwhile, quickly wipe out the frying pan and place it back on a medium heat with 2 teaspoons of olive oil and the dried chilli. Add the sliced broccoli stalk and fry for 5 minutes, or until lightly charred and golden, stirring regularly and adding small splashes of starchy pasta water, letting it bubble away before adding the next splash, and adding the sliced garlic for the final minute. Tip in the mackerel (sauce and all), breaking it up with the back of your spoon, then add 1 tin’s worth of starchy pasta water and leave to simmer for 2 minutes. Add the pasta to the broccoli and mackerel and toss everything together, loosening with splashes of the starchy cooking water, if needed. Off the heat, finely grate in the cheese, add a good squeeze of lemon juice, then toss together and season to perfection with sea salt and black pepper. Divide between plates, sprinkling over the crispy breadcrumbs and the reserved lemon zest, to serve.