When cooking courgette try and use as little liquid as possible, which is exactly why roasting is one of the best ways to go (and boiling is a no-no). Also, make sure to cook them over a high heat rather than go 'lower and slower'
You can also salt the courgette before cooking. I don't find this makes a huge difference when roasting, but if you want to try then scatter salt over the slices and leave for 10 minutes. After 10 minutes press the slices with a paper towel to remove any liquid drawn out.