Whisk water, yeast and sugar in a large bowl. Let stand until the yeast is foamy, about 10 minutes. Add flour and salt, and mix together with a wooden spoon until a shaggy dough forms. Cover bowl with a damp tea towel or plastic wrap. Refrigerate overnight for at least 10-15 hours, until dough is tripled in size.
Coat a 9x13-inch non-stick baking pan with 2 tablespoons of oil. Transfer dough to the prepared baking pan. Cover with a damp tea towel or plastic wrap. Allow to rest for 1 hour until doubled in size.
Preheat oven to 425°F for at least 30 minutes. Drizzle with remaining olive oil. Dimple dough allover with your fingers. Bake for 25 minutes, until focaccia is light golden-brown.
Top evenly with Gouda cheese slices. Continue to bake until cheese is light golden-brown, about 5 minutes. Allow to cool at room temperature for at least 10-15 minutes. Garnish with parsley. Slice and serve warm.