Add the remaining tablespoon of oil to the pan and add the garlic, ginger, and lemongrass. Fry over high heat about 30 seconds, until fragrant. Add the green beans and toss to combine. Cook, stirring occasionally, until brown spots develop and the beans are crisp-tender. Add the tofu, soy sauce, and 1/2 teaspoon of salt to the pan and toss to incorporate. Cook 1-2 minutes, until heated through, and add more salt and pepper as needed. Serve hot.