How to drain zucchini and eggplant
I think your problem will disappear with proper technique. Zucchini and eggplant are indeed full of water.  You have to both salt them well, to draw out the water, and cook them long enough for the liquid to evaporate.  

It sounds like you are both under-salting and under-cooking.  Try roasting for longer and/or at a higher temperature.  My personal favorite way to do them is on the grill, where the direct heat and lack of a 'pan' allows lots of evaporation and also delicious browning.