Lightly oil the insert of a 3-4 quart slow cooker. Spray oil works well for this.
Add the olive oil and garlic and turn the cooker to high. Let cook for a couple minutes, until fragrant.
Pour the boiling water into the slow cooker. Add salt.
Then slowly whisk in the cornmeal, stirring constantly until blended.
Cover and cook on low for 6-8 hours, stirring occasionally.
Cut the firm polenta into 1/2" slices.
Fry the slices in a bit of oil on both sides until they are starting to turn brown and the slices are heated through.
Soak the dried mushrooms in water about 30-45 minutes until they are tender.
Drain the mushrooms, reserving the water, through a coffee filter to eliminate the impurities.
Wash, pat dry, and slice the fresh mushrooms (if using).
Add the garlic to the skillet and continue cooking for a minute or so.
Simultaneously with cooking the mushrooms, in a saucepan heat the reserved liquid to boiling.
Mix the 1/2 cup of water, soy sauce, and the cornstarch until the cornstarch is dissolved and the soy sauce is blended in.
Pour the cornstarch water into the boiling liquid and stir until thickened.
Add the mushrooms and heat 5 minutes until hot.
Add salt and pepper to taste.
Serve over the fried polenta.
NOTE: Since you have to refrigerate the polenta for about 40 minutes or overnight, I suggest you do the slow cooking of the polenta the day before you want to eat this meal and refrigerate it overnight (poured into a loaf pan as instruction #6 says to do). Then finish up the recipe the next day.