Dough for wrappers
In a large bowl combine flour, oil, salt and water; mix well.
Knead until dough becomes homogeneous in texture, about 8-10 min. Cover and let stand at least 30 minutes Knead well again before making wrappers.
In a large bowl, combine all filling ingredients; mix well.
Cover and refrigerate at least an hour to allow all ingredients to impart their unique flavors. This also improves consistency of filling.
Give dough a final knead. Prepare 1-inch dough balls by taking a ball and rolling it between your palms to spherical shape.
Dust working board with dry flour. On the board, gently flatten the ball with your palm to about a 2-inch circle. Make a few semi-flattened circles; cover with a bowl.
Use a rolling pin to roll out each flattened circle into a wrapper. For well-executed momos, it's essential that middle portion of wrapper be slightly thicker than edges to ensure the structural integrity of dumplings during packing and steaming.
Hold edges of semi-flattened dough with one hand, and with the other hand, begin rolling edges of dough out, swirling a bit at a time. Continue until the wrapper attains 3-inch diameter circular shape.
Repeat with remaining semi-flattened dough circles. Cover with bowl to prevent from drying.
For packing, hold wrapper on one palm, put in one Tbsp filling mixture and with the other hand, bring all edges together to the center, making pleats.
Pinch and twist pleats to ensure closure of stuffed dumpling. This holds the key to good tasting, juicy dumplings.
Heat up a steamer and oil the steamer rack well. This is critical because it will prevent dumplings from sticking.
Arrange uncooked momos in steamer. Close lid and allow steaming until dumplings are cooked through, about 10-15 min.
Take dumplings off steamer and immediately serve. To serve, arrange cooked momos on a plate dressed with tomato achar.