Place the center-cut bacon in a cold skillet and heat to medium, cooking until the fat renders and the strips are perfectly crispy.
Remove the bacon to a paper towel to drain, then discard most of the fat from the skillet, leaving just a light coating.
In a small bowl, whisk together the whole egg, liquid egg whites, sea salt, and black pepper until well combined.
Pour the egg mixture into the skillet and cook over medium-low heat, folding the edges inward to create a square patty shape.
While the eggs cook, toast the sprouted grain bread slices until golden and firm.
In a small ramekin, stir together the nonfat Greek yogurt and Dijon mustard to create a creamy, tangy spread.
Spread the yogurt mixture onto one slice of toast, then layer on the fresh baby spinach.
Place the cooked egg patty on top of the spinach, followed by the sharp cheddar cheese and crispy bacon strips.
Top with the second slice of toast and slice diagonally to serve while the cheese is melting.