Fry bacon in a large skillet over medium-heat until crispy; about 4 minutes on each side. Transfer bacon to a paper towel lined plate. Add eggs to the same pan (in the bacon fat) and fry or scrambled. Transfer eggs to a paper towel lined plate.
In a small bowl whisk together the yogurt, mustard, and salt. Add mustard or salt if needed to reach your desired taste.
Spread a 1/2 tablespoon of the mustard mixture on each piece of toast, then layer two of the pieces with the arugula, tomatoes, bacon, eggs, salt, pepper, and lemon zest. Top with the other slice of bread, cut in half, and serve!