The tomatoes, potatoes and zucchini need to be roughly the same diameter, in order to make a more beautiful arrangement. Make a sauce at the bottom of the tray, as follows:
Grate several tomatoes, dice the onions and pepper. Add the tomato paste.
Braise everything, add the spices and leave the sauce aside. If it's too thick, add a little water.
Distribute the sauce along the bottom of the tray and begin arranging slices of tomatoes, potatoes and zucchini.
It doesn't matter which vegetable you start with, just be sure to alternate between them all the way to the end.
Bake at 356°F (180 °C) under foil. After 30 min., take the foil off and bake to a crisp.