Soak beans overnight in cold water. In the morning, rinse them well.
Put water to a boil in a medium-sized pot. Add bay leaf, salt, and beans and boil them for 40 minutes (or until fork-tender). Strain the beans and put them in a bowl.
In the meantime, chop finely onion and garlic cloves. If you use fresh mushrooms, slice them too.
Preheat a skillet. Reduce the heat and add a tablespoon of vegetable oil. Place onion and garlic in the skillet and fry them until golden.
Mash the beans in a pure. Add avocado oil, black pepper, nutmeg, and ½ of the walnut pieces (keep the other half for decorating the pate). Put the mixture aside to cool.
Combine fried onion and garlic with the bean mixture. Mix well and add salt to taste.
Place baking paper on the cutting board. Transfer the bean paste onto the baking paper with a spoon and roll it, as if you were making a sausage. Put the bundled-up pâte in the freezer for an hour.
Now, it is time to fry mushrooms. Put the sliced mushrooms in the preheated skillet and fry them for 10 minutes. Salt to taste.
Slice pickled cucumbers.
Remove the bean paste from the freezer, unwrap it, and slice it.
Arrange the pâte slices on a big plate, top them with the remaining pieces of walnuts, and put thin slices of pickles in between. Sprinkle the dish with parmesan cheese.
Garnish the dish with mushrooms and serve cold.