Slice your bacon into ¾ inch strips. This is easier to do with very cold bacon, so I recommend putting it in the freezer for 15 minutes before slicing it.
Cook your bacon in a large non-stick pan until it is browned and crispy. This should take about 10 minutes.Use a slotted spoon to transfer the bacon from the pan to a paper-towel lined plate to drain. Reserve the bacon grease in a small bowl.
Heat 1½ tablespoons of the reserved bacon grease in the bacon pan and add the mushrooms and onions. Sauté for about 5 minutes until the mushrooms are tender. Set aside and keep warm while you prepare the bacon vinaigrette.
Heat 1 tablespoon plus 1 teaspoon bacon grease in a small pan. Whisk in the Dijon, vinegar and brown sugar until smooth. Season with salt and fresh ground pepper to taste.
Fry your eggs in a non-stick pan until the whites are set, but the yolks are still runny. If you want to get crazy, fry them in the remaining bacon grease.
Divide the spinach among two plates or bowls. Drizzle each with bacon vinaigrette and add the warm mushrooms and onions. Top each salad with a fried egg and serve immediately.