Pour the oysters into a colander set over a bowl. Let drain while preparing the flavorings.
In a very large (12-inch) skillet, melt the butter of medium-high. Add the onion, tomato and serrano, and cook, stirring frequently, until the onion is translucent and the juice from the tomatoes has evaporated, about 5 minutes.
Add the white wine, soy, crema (or its substitute), parsley and 1⁄2 cup juice drained from the oysters. Cook until as thick as a light cream soup, about 5 to 6 minutes. Add the oysters, reduce the heat to medium and cook, stirring frequently, until the oysters are just barely cooked, about 3 minutes. Stir in the cheese, taste and season with salt, usually about a scant 1⁄2 teaspoon.
Spoon into warm dishes and serve right away with a sprinkling of parsley.