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 hoisin sauce, chili garlic sauce, soy sauce, vinegar, cornstarch, and water water, together in a small bowl. Set aside.
Stir-Fry: Warm the oil in a large sauté pan, large skillet, or wok over medium heat, then fry the white parts of the green onion, garlic, and ginger for 3-5 minutes. Whisk the hoisin sauce well to make sure the cornstarch is dissolved, then pour into the pan. Bring to a simmer and cook for 3 to 5 minutes, until the sauce is thick and glossy. Add the cooked tofu and sesame seeds to the pan and mix well; cook for an additional 1 to 2 minutes, until warmed and coated evenly in sauce.
Serve: Serve warm over rice and vegetables (or as desired) and topped with the remaining green onions. Leftovers will keep in the fridge for up to 5 days.