Preheat the oven to 325 degrees F. (160 degrees C.).
Place the beans in a large saucepan with plenty of water and allow to simmer for 2 hours along with the peeled tomatoes, sage, rosemary, garlic, pepper and chili powder. Add salt once the beans are cooked.
Gently wash the mushroom caps with running water, protecting them with your hands so as to prevent them absorbing too much of the water.
Place the mushrooms on a sheet of aluminum foil on a baking tray. Slice the garlic and gently insert each piece into the mushroom caps. Sprinkle the chopped nipitella over the mushrooms and add salt, pepper and a generous dash of olive oil.
Wrap the mushrooms in the aluminum foil, carefully ensuring all the edges are sealed and place on a baking tray in a shallow bath of water. This is now ready to be cooked 'bain marie' style for 20 minutes.
Once the mushrooms are cooked, assemble them onto a plate with two large tablespoons of the cooked beans and some small shavings of crusty bread. Drizzle with olive oil and serve the dish piping hot.