Prepare the filling by combining the ground chicken, minced red onion, ginger, garlic, cilantro, cumin, turmeric, sea salt, and black pepper in a large mixing bowl.
Place a small spoonful of the chicken mixture in the center of each dumpling wrapper.
Moisten the outer edges of the wrapper with a small amount of water, then pleat and pinch the edges together to seal the dumpling into a crescent or round shape.
Arrange the momos in a steamer basket lined with parchment paper, ensuring they do not touch each other.
Steam the momos over boiling water for 10 to 12 minutes until the chicken is fully cooked and the wrappers appear translucent.
While the momos steam, prepare the achar by charring the tomato in a dry skillet or over an open flame until the skin blisters and blackens.
Peel the charred tomato and blend it with the sesame oil, chili flakes, and lemon juice until a smooth, thick sauce forms.
Serve the hot steamed momos immediately with the smoky tomato achar on the side for dipping.