Wash potatoes and slice about 1/8" thick. Slice onion into half-moons.
Heat an oven safe saute pan over medium heat with 1 tablespoon olive oil. Fry the potatoes in batches that will fit on the bottom. Fry until they are soft and translucent, but not crispy. Add more oil as necessary for each batch. When the potatoes are done fry the onions in the same way until they are translucent and soft but not crispy or dark.
Preheat the broiler.
Beat the eggs and the salt together. Arrange the potatoes in the pan over the onions. Do the same with the asparagus and zucchini. Pour the egg mixture over top and cook until the bottom becomes firm.
When the bottom is firm transfer to the broiler for approximately 5 minutes, or until the omelette becomes firm and is golden on top. Remove and let stand for at least 5 minutes to cool and set.
May be served warm or cool.
There are 439 calories in 1 serving of Spanish Tortilla II.