1.Put the zucchini in a fine sieve over the sink, use your clean hands to squeeze any extra liquid from the zucchini. Put the carrot, zucchini, onion, cheese and mayonnaise in a medium bowl, mix them together with a wooden spoon.
2.Spread the bread slices with the butter. Spread the vegetable mixture over four of the bread slices, put the other four slices on top.
3.Use a serrated bread knife to cut off the crusts, cut the sandwiches in half.
Zucchini have a lot of water in them; squeezing the water out of the grated zucchini, prevents the sandwiches from getting soggy. For information about how to grate a carrot see page 121. Put the grated zucchini in a fine sieve over a small bowl. Use your hands to squeeze the liquid out. Use a serrated bread knife to cut the crusts off the sandwiches. Cut the sandwiches in half. Spread the vegetable mixture onto four of the bread slices then top with the rest of the bread slices.