heat vegetable oil and half of sesame oil in soup pot. when hot, add garlic, ginger, chile, and cilantro. stir-fry for 2 minutes. add broth, five-spice powder, and salt. bring to a boil, then lower the heat and simmer, covered, for 15 minutes. strain and return to the pan, or simply lift out the chopped flavorings with a small skimmer. press out as much liquid as you can, then discard.
add sweet potatoes to the pot and simmer, covered, for 10 minutes or until tender when pierced with a knife.
add greens and tofu. cook gently, uncovered, until the greens are bright and tofu is hot, about 5 minutes. add scallions. taste for salt and add remaining sesame oil. add soy sauce to taste, if dish seems to need a little extra punch.