Cut the tofu in half lengthwise down the top. Slice into squares 1/4 inch thick. Stir together the soy sauce, vinegar, sesame oil, and sugar in a small bowl, set aside.
Heat oil in a large, nonstick pan over medium heat. Add garlic and green onions, and cook until fragrant, about 20 seconds. Brown tofu well on each side, then pour in sauce and cook until the sauce has been incorporated by the tofu, 2 to 3 minutes. Season to taste with salt and pepper.