In a medium non-stick skillet over medium heat, gently sweat the onions in the butter, for about 20 minutes, or deep golden brown -- be careful not to burn. Transfer to a plate. Wipe the skillet clean.
In a medium bowl, whisk the eggs and water. Season with salt and pepper. Melt the butter over low heat. Add the eggs to the pan and leave them be for 2 minutes. With a rubber spatula or wooden spoon, gently scrape the eggs from the bottom of the pan. Let them cook another minute or so, then scrape again -- do not move them too often. Continue at this slow pace until the eggs are no longer runny and holding together. Remove from the heat.
Lay a tortilla on a work surface. Spoon a few tablespoons of the scrambled eggs down the center. Drizzle a teaspoon of the hot sauce along the eggs. Add a few tablespoons of the onion, then a few tablespoons of the cheese. Roll. Repeat with remaining tortillas.