1Heat a grill pan or outdoor grill to medium high (about 375°F to 425°F).
2Meanwhile, arrange the bread slices in a single layer on a baking sheet. Using 1 tablespoon of the oil, very lightly brush the tops of the bread with the oil. Flip the slices over and brush with the remaining 1 tablespoon oil. Generously season one side only with salt and pepper.
3Place the bread on the grill (reserve the baking sheet) and cook until grill marks appear and the bread is toasted and crisp, about 2 to 3 minutes per side.
4Return the grilled bread to the reserved baking sheet, seasoned-side up, and rub the seasoned sides with the garlic clove. Set aside while you make the topping.
For the topping:
1Place the oil and pancetta in a large frying pan over medium heat and cook, stirring occasionally, until the pancetta is crisp and browned, about 10 minutes. Using a slotted spoon, remove the pancetta to a paper-towel-lined plate and set aside.
2Increase the heat to high, add the mushrooms and thyme, and cook, stirring rarely, until the mushrooms are golden brown, about 7 to 9 minutes. Remove the pan from the heat, add the wine and vinegar, and scrape up any browned bits stuck to the bottom of the pan until the liquid has been absorbed, about 30 seconds. Return the pan to low heat, stir in the cream, and cook until the sauce thickens slightly, about 2 minutes. Add the reserved pancetta and stir to combine. Taste and season with salt and pepper as needed.
3To serve, divide the mushroom mixture evenly over the grilled bread and cut the bruschetta into pieces if desired before serving.