Preheat the oven to 400°F (200°C).
Lightly grease or line a medium baking dish.
In a mixing bowl, combine the oats, eggs and sour cream and stir until smooth.
Add the water, salt and thyme and mix again.
Fold in the finely chopped onion and shredded mozzarella until evenly distributed.
Pour the mixture into the prepared baking dish and spread it into an even layer.
Bake for about 20 minutes, until the top is golden and the centre is set.
Let the bake rest for a few minutes, then slice and serve warm.