Ok...there's many ways to make an omelette but this one is a meal. Based on the Spanish tortilla it has potatoes as its main vege but then you can add what you want: in this case it's corn, zucchini and capsicum. I often add chopped chilli or tabasco too.
Beat the eggs, milk, salt and pepper in a bowl and set aside.
Heat the olive oil in a medium sized heavy frying pan over medium heat and fry the garlic and potato slices till coated, about 2 mins. Add the water and the stock cube and cook, uncovered, for 10 minutes so that most of the water should have evaporated but there will still be a little water in the pan.
Pour in the egg mixture and arrange the zucchini slices, capsicum slices and corn kernels on top of the egg. Sprinkle the grated cheese on top. Turn the heat down to medium-low, cover and cook for 10-15 minutes. Check occasionally and if large bubbles have appeared in the tortilla break them up with a knife. Also run a blunt knife around the edges and move the frypan around on the heat to make sure the cooking is even.
Once there are no more runny bits of the tortilla on the top, place the frypan under a preheated grill for a few minutes to finish off the cooking. When the top has browned removed from the grill, let sit for a couple of minutes then serve in slices.