In a small skillet, heat olive oil. Once hot add the mushrooms and sprinkle with salt. Cook until mushrooms are soft and they have released all their liquid.
While the mushrooms cook, toasted the bread to desired done-ness.
Top each slice of toast with arugula and tomato. Once mushrooms have finished cooking, place the mushrooms on top of the tomato. Gently lay the poach egg on top of the mushrooms and sprinkle with coarse ground pepper.