In a bowl combine the ricotta, cheddar cheese, eggs, thyme, remaining lemon juice and lemon zest.
With the washed zucchini you want long, thin slices, as long as possible and as rectangular in shape as possible. They need to be thin enough to use like fresh lasagne sheets. You can slice by hand, use a wide peeler or use a vegetable slicer.
Roll a piece of zucchini into a circle and place into the tomato base, start against the edge. Fill the centre with ricotta mixture. Continue until all the ingredients have been used.
Fill any gaps with remaining tomato mixture. Gently sprinkle each one with parmesan and the reserved cheddar cheese.