Soak the porcini mushrooms in 1 1/2 c of warm water for at least 30 minutes. Drain in a sieve lined with cheesecloth, reserving the liquid for use elsewhere. Squeeze the porcini & wash in fresh water. Cut into very fine pieces.
Clean fresh mushrooms with a damp cloth & dice them. Place in a medium- sized bowl. Add the porcini, tomatoes, rosemary, sage, garlic & pepper. Mix together well. Toss with the lemon juice & oil. Cover & leave for 24 hours.
Just before serving, add the salt. If it seems to be too moist, then drain off the extra moisture.
Use as an appetizer salad or as a topping fro grilled bread. Or omit, the lemon & use as a pasta sauce.