First get your largest pan filled, yes filled, with water. Salt it well. Bring to the boil.
Meanwhile, thinly slice garlic and dice your courgettes. Warm the oil over a low to medium heat and gently cook your garlic - stir and don't let it colour - for about 5 minutes. Add your diced courgettes, turn up the heat to medium and cook for another 5 minutes, stirring. Watch that your garlic doesn't burn.
Your pasta water should be boiling by now so toss in the penne and let it boil for a minute or two less than it says on the packet. Just before you drain the pasta, scoop out and reserve half a mugful of starchy water - this is to mix in afterwards.
Add the butter, chilli (if using), zest and juice of half a lemon, salt and pepper and parsley to the courgettes, stir well, add a lid to the pan and cook gently for 5 minutes more over a medium heat. Then taste, season again if required.
Drain pasta and tip back into the large pan. Add your courgette mixture and splash a few tablespoons of water in. Mix well. Throw in half of the cheese and toss again. You may need a little more water. Taste again and if happy, serve with more cheese at the table. This dish lives or dies on its seasoning and generous amount of parmesan so don't be backwards in coming forwards!