Heat a grill pan over high heat. Drizzle chicken thighs with oil, season with salt, pepper and rosemary. Grill chicken 5 minutes on each side and remove from heat to rest for 5 minutes.
Place stock in a small bowl and cover. Heat in microwave on high for 2 minutes. Remove stock from microwave with oven mitt. Add dried porcini to the dish and replace the cover. Steep porcinis in stock 5 to 10 minutes to reconstitute mushrooms. This may also be done on the stovetop. Simmer broth, and mushrooms for 10 minutes over low heat.
In a medium skillet, add 2 tablespoons olive oil, saute pancetta, crushed garlic and chopped shallot over medium heat for 3 minutes, to crisp pancetta at edges. Add sliced portobello mushrooms to the pan and season with salt and pepper. Saute mushrooms 10 minutes, or until dark and tender. Add flour and cook 1 minute. Add red wine to the pan and reduce by 1/2, about 1 minute. Add reserved stock and porcini mushrooms to the pan and simmer together 1 to 2 minutes longer to combine.
Slice chicken thighs and fan out on a plate. Ladle thick mushroom sauce down over sliced chicken and serve.