To press the tofu: either use a tofu press and press the tofu for at least 1 hour. Or, place the block of tofu onto a clean kitchen towel, then place a second towel on top and either use your hands to press the liquid out, or place a heavy pot on top and let it sit for 20 minutes or so. Then, slice the tofu into 1" cubes.
Place the pressed tofu into a plastic bag or a bowl, then add the soy sauce and cornstarch, seal the bag, and shake until the tofu is coated. If using a bowl instead, gently stir to combine.
Next, heat 1 tablespoon of oil in a large, nonstick skillet over medium heat. Once it starts shimmering, add the tofu and pan-fry it until it's golden brown and crispy on all sides.
While the tofu is cooking, make the sauce: whisk all sauce ingredients together in a glass measuring cup and set aside.
In a separate skillet, heat 1 tablespoon of oil over medium heat, then add the broccoli and sauté for 2 minutes before adding 2-4 tablespoons of water and cooking until it's fork tender. Then, add a little more oil, along with the spinach and garlic and cook until the spinach is soft, 1-2 minutes.
Once the tofu is done cooking, reduce the heat to low and pour in the sauce, stirring until the tofu is coated. If the sauce is thickening too quickly, remove the skillet from the heat and add 1 tablespoon of water. If it isn't thickening quickly enough, turn the heat back up to medium.
Assemble the stir fry: divide the rice into two bowls, then top it with the tofu, broccoli and spinach. Sprinkle with green onions and enjoy!