Step 1

Brush both sides of ciabatta slices lightly with 1 tablespoon olive oil. Lightly toast slices in oven or toaster oven until golden.

Step 2

Heat remaining 2 tablespoons olive oil in large nonstick skillet over medium heat. Add onion and season with salt and cook stirring occasionally, until onion is softened, about 4 minutes. Add mushrooms and cook until softened, about 3 minutes. Increase heat to medium high, add balsamic vinegar and cook, stirring frequently, until most of the liquid is absorbed, about 3 minutes. Stir in thyme. Remove from skillet and keep warm.

Step 3

Heat same skillet over medium-high heat. Cook steak in 2 batches, stirring frequently, until browned outside and desired doneness inside.

Step 4

To serve, arrange steak over toasted ciabatta and top with mushroom mixture. Garnish with additional thyme if desired.