Mix about 100g quick cooking polenta (i use the 1 or 2 minute varieties when im in a rush and don't want to spend 25 mins stirring!) with approx 400ml water and cook according to directions on packet. The amount of water will depend on the brand and how precooked it is. When all the water is absorbed, poor into the bottom of a baking dish (or two) and smooth out with a spatula. You want to get it as thin as possible and want it no more that 1cm high. Put in fridge to cool while you chop the vegies. If you have more time you can make two batches, or use two baking dishes the same size and make both at once.
Chop vegies as thin as you can get them. I tried for around 1mm thick.
Prepare a tomato sauce however you like it (onion, garlic, herbs all optional). I had some leftover in the fridge, but if you're short on time you can also use bottled tomato puree.
Putting it all together
Once the vegies are chopped get the polenta out of the fridge and tip out onto a tray or baking paper, being careful not to break it. Using the same baking dish, layer the tomato sauce and vegetable. If you have enough for two layers of polenta add the first one in the middle of the layering process and add the other at the end. I only had enough for one polenta layer so I used this for the top.
Add a little more tomato sauce on the top polenta layer, add some grated cheese, and cook at about 180 degrees for around 45 mins to an hour. When done, a skewer should push through the vegetables easily.