Place a non-stick skillet over medium hight heat. Add 1 tbsp butter and the olive oil. When the butter is melted and the skillet is hot, add the mushrooms. Sprinkle with a little kosher salt. Sauté the mushrooms for 3 to 4 minutes until they begin to release their moisture, stirring occasionally. Continue cooking the mushrooms until the liquid evaporates and the mushrooms begin to brown, about 3 to 4 more minutes.
When the mushrooms are browned, add the garlic and sauté for another minute and then add the spinach. Toss the spinach in the skillet with the mushrooms until wilted. Season with kosher salt and pepper to taste. Set aside and keep warm, transferring out of the skillet if you need it to cook the eggs.
Place a non-stick skillet over medium heat and add the remaining 1 tbsp of butter. Add the eggs and cook according to your preference, either sunny side up or over easy. Season with kosher salt and pepper.
Toast the bread and lightly butter if desired. Arrange each piece of toast on plate and top with the mushrooms and spinach. Top each toast with an egg and garnish with chopped chives if desired. Enjoy!