Preheat oven to 375 degrees F. Heat a cast-iron or nonstick ovenproof skillet, and cook bacon according to package directions; remove and drain on paper towels. Reserve a tbsp. or two of the grease, and heat on medium-high. When hot, add the onions and mushrooms, stirring frequently until the onions are soft and the mushrooms release then reabsorb their liquid, about 5-10 minutes.

Add the asparagus stalk and saute for another 2 minutes, then add spinach and stir frequently, until spinach is just wilted, about 1-2 minutes.

Whisk the eggs in a bowl. When the vegetables are done, turn off the burner and stir in the eggs until just mixed, then season with salt and pepper. Eggs will cook a little. Put skillet in oven, and heat until the eggs are cooked through, 5-10 minutes.

Serve topped with tomatoes and crumbled bacon.