Mix the flour, water, and salt into a smooth dough. Knead for 5 minutes, cover, and rest for 20 minutes.
Combine the ground chicken, cabbage, scallions, cilantro, ginger, garlic, soy sauce, and sesame oil in a bowl.
Shape and Steam:
Roll the dough into a rope and cut it into 24 pieces. Roll each piece into a thin round, keeping the center slightly thicker than the edge.
Add a spoonful of filling to each wrapper, pleat or fold to seal, and arrange in an oiled steamer basket. Steam over simmering water for 12 to 15 minutes.
Make Achar and Serve:
Blend the tomatoes, sesame seeds, lime juice, cumin, and a pinch of salt into a textured sauce.
Serve the hot momos immediately with the tomato achar.
Notes
Do not overcrowd the steamer; leave space between dumplings so steam can circulate.
Vegetarian momos work well with finely chopped cabbage, mushrooms, carrots, and tofu.