Cut the potatoes into small bite-sized pieces. Put them in a pan of cold water, bring to the boil, then gently simmer for about 12 minutes until tender.
Drain, then put them back in the pan.
Meanwhile, grate the courgette and slice the garlic.
Heat the oil and sauté the garlic for a minute then add the grated courgette and stir for a minute.
Season with salt and pepper and add the lemon juice and zest.
Add the potatoes and cook for another couple of minutes, stirring constantly.
Finally, crumble the cheese on top (if used) and toss.
Serve warm.