Preheat oven to 375 degrees. Cut the baguette crosswise into 16 (1/4-inch) thick slices; place on a baking sheet. Brush the bread with olive oil and season with salt and pepper. Toast in the oven until golden brown, about 8-10 minutes. Set aside to cool. Heat 3 tbsp of olive oil in a large skillet over medium heat. Add the sliced shallot and cook, stirring, until soft, about 3 minutes. Add mushrooms and cook, stirring occasionally, until tender and any juices have evaporated, about 7-10 minutes. Season mushroom mixture with salt and pepper. Place a wedge of cheese on top of each crostini and top with a tablespoon of mushroom mixture. Sprinkle with chives, and serve warm.