Prep: Preheat the oven to 425F and line a baking sheet with a silicone mat or parchment paper. Tear the tofu into bite-sized chunks for a more meat-like shape and texture, or cut into small cubes.
Tofu: Add the tofu to a medium bowl and add in the oil and tamari. Toss with a spatula until evenly coated, then sprinkle the cornstarch on top and toss again. Transfer to a baking sheet and spread out the tofu pieces so they aren’t touching. Bake on the top rack of the oven for 30 minutes, flipping the tofu halfway through.
Sauce: Whisk the gochujang, soy sauce, sugar, ginger, cornstarch, and water together in a small bowl. Set aside.
Aromatics: Add the avocado oil to a large sauté pan over medium heat. Once warm, add the white parts of the green onion, garlic, and gochugaru, if using; sauté for 1 to 2 minutes.
Make it Saucy: Pour the sauce into the pan and bring to a simmer, stirring well. Cook for an additional 3 to 5 minutes, until the sauce has thickened to your liking.
Final Touches: Turn the heat to low, then stir in the baked tofu, green portions of the green onions, toasted sesame oil, and sesame seeds. Divide the tofu between serving bowls and serve warm, with vegetables and rice or as desired. Leftovers will keep in the fridge for up to 5 days.