Brown the breakfast sausage in a medium skillet over medium heat, breaking it up with a wooden spoon, about 6 minutes.
Whisk together the eggs, milk, mustard and a pinch of salt in a large mixing bowl.
Cut a long oval down the center of each bread, about 2 inches wide and 4 inches long. Hollow out most of the insides, like a canoe, leaving about 1/2-inch border all the way around. Place on a baking sheet, then gently pour half the egg mixture into each "boat." Sprinkle with the browned breakfast sausage and a few pinches of chopped kale, then top with remaining egg mixture.
Top each boat with the shredded Cheddar, and bake until the cheese is browned and bubbly and eggs are just set, between 25 to 35 minutes. Let cool about 5 minutes, then garnish with parsley and serve!