Combine the parsley, onion, 3 tablespoons of the lemon juice, 1/2 teaspoon of the chili powder, 1/2 teaspoon salt and a couple turns of pepper in a small bowl. Cover and refrigerate until needed or for up to 1 day.
Heat the oil in a large skillet over medium-high heat. Add the carrot, coriander, nutmeg and remaining 1 tablespoon chili powder. Cook until the spices are fragrant and the carrot begins to soften, about 1 minute. Add the ground chicken and sprinkle with 3/4 teaspoon salt and a couple turns of pepper. Cook, breaking up the chicken, until it begins to brown, about 5 minutes. Add 1/2 cup water, bring to a simmer and cook until slightly thickened, about 5 minutes. Remove from the heat.
Mix the yogurt with the remaining 2 tablespoons lemon juice. To assemble the tacos, scoop the chicken mixture into the tortillas, then top with some onion salad and sprinkle with parsley. Serve with the yogurt and lemon wedges.