Drain extra-firm tofu well in a colander placed in the sink. Then cut tofu into two thinner pieces, and put the tofu between a double layer of paper towels. Put a heavy pan or some kind of weight on top of the tofu and let it press out the water for 10 minutes, or a bit longer if you have plenty of time.
While tofu gets pressed, mix the soy sauce, rice vinegar, sesame oil, and red pepper flakes to make the marinating liquid.
Cut the extra-firm tofu into 1 inch cubes. Put tofu into a zip-loc bag and add the marinade, and marinate the tofu for 30 - 60 minutes or longer. (You can even marinate the tofu all day while you're at work if you really want to add flavor.)
After it marinates, let the tofu drain well in a colander placed over a bowl to catch the marinade.
Put the marinade you drained off into a measuring cup and mix in the Monkfruit sweetener and sugar-free preserves.
Heat the dry wok over high heat; then add 1 tablespoon of peanut oil and heat until shimmery.
Add the sliced garlic and ginger and cook just until fragrant; then remove and discard garlic and ginger. (This only takes a minute or two; don't let the garlic burn!)
Lower heat to medium-high, immediately add the drained tofu and cook, turning often, until it's well browned. This will take about 5-7 minutes but watch carefully; it's easy to get some pieces that are a bit dark.
While tofu cooks, cut mushrooms in pieces that are close to the size of the tofu.
Remove tofu, turn heat to high, add the rest of the oil, add mushrooms, and cook until they are cooked through and all liquid has evaporated, about 4-5 minutes.
Add the tofu back into wok with the mushrooms. Stir to gently combine.
Add the marinade mixture with the added ingredients, lower heat to medium high, and cook, stirring a few times, until all the ingredients are slightly glazed and the mixture has slightly thickened, about 2-3 minutes.
Add the sliced green onions and cook 1 minute more.
Serve the Tofu Mushroom Stir Fry hot, and enjoy!
I refrigerated the leftovers overnight, and the next day I heated them in a small frying pan with about a teaspoon of oil, and the leftovers were great!