Preheat oven to 350 degrees F.

In a small mixing bowl, whisk together the ground flaxseed and water. Set aside.

Into a medium-size mixing bowl, add the thawed and well-drained spinach, seasoned bread crumbs, Parmesan cheese, butter, yellow onion, garlic, and flaxseed mixture. Stir to combine.

Using your hands or a cookie scoop, shape the mixture into 1-inch balls. Onto a large baking sheet, arrange the balls in a single layer.

Set in the preheated oven to bake for 20-25 minutes, until lightly browned and firm to the touch. Allow to cool 5 minutes before serving.

Serve warm or room temperature.