Place 5 teaspoons oil and shallots in a large skillet over medium-low heat. Cook until the shallots start to brown, 4 to 6 minutes. Add garlic and cook, stirring, until fragrant, about 15 seconds. Add mustard greens, dates and 2 tablespoons water and cook, stirring occasionally, until the greens are tender and the water evaporates (add another tablespoon of water if the pan is dry before the greens are tender), about 4 minutes. Stir in vinegar, salt and the prepared bulgur; cook until heated through, about 1 minute. Drizzle with the remaining 1 teaspoon oil and sprinkle with the walnuts before serving.