If you're on the Paleo diet and craving an Egg McMuffin, this sandwich should do the trick. Instead of bread, we used hearty Portobello mushroom caps. Make sure you mash the avocado enough so that it doesn't slip out of the Portobello.
Preheat oven to 450°F. Place mushroom caps on parchment-lined baking sheet and drizzle with olive oil. Add salt and pepper to taste. Bake in oven for 7 minutes per side.
Meanwhile, fry bacon slices in a skillet over medium heat until crispy. Remove bacon and allow to drain on a paper-towel lined plate. Add eggs to greased skillet and cook over medium-low heat until whites are set and yolks begin to thicken.
On 2 mushroom caps, layer avocado, tomato slices, arugula, fried egg, and bacon. Top with mushroom caps.