Preheat the oven to 400 degrees. Line a baking tray with parchment.
Slice the tofu into two even-thickness pieces and press the water out using a few layers of cheese cloth or paper towel (make sure it is very dry). When the oven is heated, cut the tofu into 1/2-inch pieces. Season both sides with sea salt. Bake for about 30 minutes, until the tofu turns golden and the surface puffs.
Meanwhile, heat oil in a wok or large sauté pan over medium heat.
Add the green beans and stir fry them for 3-5 minutes or until they start to shrivel up a bit.
Add the garlic, scallions and hot sauce, if desired. Stir to combine. Cook for 30 seconds to a minute then add the soy sauce, rice vinegar, sugar, water and chili flakes. Cook an additional 1-2 minutes or until most of the liquids are cooked off. Toss with the crispy tofu and garnish with sliced scallion and sesame seeds, if desired.