If you have the opportunity, fully freeze and then thaw the tofu in the days before making the recipe. While this isn't required, it does produce a better texture. When you're ready to make the recipe, remove the tofu from the package and press or squeeze the excess moisture out of the tofu. You can use a tofu press, or place the tofu on a plate, top it with a cutting board, then place something heavy, like a pot, and wait about 15 minutes while the moisture is pressed out. When tofu has been frozen, it's a bit more spongey, and I can squeeze or press most of it out just using my hands.
While the tofu is pressing, clean and slice the mushrooms. Thaw the frozen spinach, then squeeze out the excess water (I just squeeze it in my fist).
Add the cooking oil to a large skillet and place it over medium heat. When the skillet and oil are hot, tilt the skillet to coat the surface with oil. Crumble the tofu into the skillet, then sprinkle the garlic powder and pepper over top. Sauté the tofu for 2-3 minutes in the hot skillet. Don't worry if it starts to stick, the moisture from the vegetables will loosen it from the bottom of the skillet.
Add the mushrooms and continue to sauté until the mushrooms have softened. Add the frozen bell peppers and onions and continue to sauté until they have heated through. Finally, add the thawed and squeezed spinach, and continue to sauté until heated through again.
Finally, season the skillet with nutritional yeast and salt. Toss until everything is well coated in nutritional yeast. Give it a taste, and adjust the salt if needed.
Serve the vegetable tofu scramble topped with a couple of spoonfuls of salsa, and enjoy!