Microwave the riced cauliflower for 2-3 minutes, until tender. (Alternatively, you can steam it.) Set aside to cool.
Meanwhile, whisk together the shredded onion, golden flaxseed meal, garlic salt, egg, and one egg white in a large bowl.
When the riced cauliflower is cool enough to handle, wrap it in a cheesecloth or towel. Squeeze tightly over the sink to drain as much moisture as possible. (I drained more than a cup of liquid.)
Stir the cauliflower into the bowl with the other ingredients. If it doesn’t stick together well when trying to form a patty (i.e. if your head of cauliflower was very large), add another egg white.
Heat a generously oiled skillet over medium heat. Drop tablespoonfuls of the cauliflower mixture onto the pan and press down with a spatula to form hash brown patties. Cook for 2-4 minutes, until the bottom is browned, then flip and repeat for 2-4 minutes on the other side. Repeat with the remaining cauliflower mixture.