Heat the olive oil in a pan that has a cover. When the oil is hot, add the mushrooms, salt and sherry. Cover, and lower heat. Cook until liquid is released from the mushrooms, about 10 minutes. Drain and set aside.
Toast bread slightly, just to dry it out a bit. Spread with alioli and top with mushroom and sliced tomato. Broil for about 30 seconds or until alioli starts to bubble. Add a bit of feta if desired.