2. Arrange mushroom slices in a single layer on a large baking sheet. Drizzle the mushrooms with olive oil and toss. Sprinkle the mushrooms with thyme, salt, and pepper. Toss again.
3. Roast the mushrooms, stirring halfway through, for 20 minutes or until they are hot and beginning to brown around the edges. Remove from oven and set aside.
4. Turn the oven to broil. Place the bread slices on a baking sheet and toast for 2-3 minutes. Remove the pan from the oven and flip the bread over, toast for an additional 2-3 minutes. You just want to get the bread toasted. Watch carefully so it doesn't burn. Remove the pan from the oven.
5. Take the garlic clove and spread it over each slice of bread. This will give the bread a nice garlic flavor. Top each slice of bread with roasted mushrooms. Top with shredded gruyere cheese. Place the pan back in the oven under broil for 2 minutes, or until the cheese melts. Again, watch it closely. Garnish with extra thyme, if desired. Serve warm.