In a large bowl, combine the ground chicken, finely minced red onion, shredded cabbage, chopped cilantro, grated ginger, minced garlic, cumin, coriander, sea salt, black pepper, and sesame oil.
Mix the filling thoroughly by hand until the ingredients are well incorporated and the mixture becomes slightly tacky.
Place a wonton wrapper on a clean surface and add a rounded tablespoon of the chicken mixture to the center of the wrapper.
Lightly moisten the edges of the wrapper with water, then pleat and fold the edges together to seal the dumpling into a tight circular or half-moon shape.
Arrange the momos in a steamer basket lined with parchment paper or cabbage leaves, ensuring they do not touch each other to prevent sticking.
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, roast the whole tomato and green chili over an open flame or in a dry pan until the skins are charred and blistered.
Blend the charred tomato, chili, toasted sesame seeds, turmeric, and a pinch of salt until a smooth, vibrant dipping sauce forms.
Serve the hot momos immediately with a generous side of the smoky tomato achar for dipping.