In a chopper or food processor, pulse the pumpkin and onion separately, not too finely, still in small chunks. Alternatively, cut into small cubed pieces. Mix together with the meat, salt, pepper, oil and water, using your hands, until combined. Set aside.
Mix dough ingredients together and knead on the counter for about 5 minutes, until dough it's a smooth ball. Let the dough rest for half and hour and give it a good knead again for a few minutes. Cover with a bowl and let it rest for at least 1 more hour.
Cut dough into pieces. Using a rolling pin, roll out the dough into a thin layer (about ⅛"). It's much easier to use a pasta roller, or I use a KitchenAid Mixmaster pasta roller attachment. Take the cut piece of dough, roughly roll with a rolling pin until it's able to be rolled through the pasta maker. First time, I rolled it on a thicker setting #1, then follow through with a thinner setting #2, which gets you to the desired thickness. Sprinkle flour on the pasta pieces to prevent them from sticking to the table.
Use a large can or a glass for cutting the shape of the dough circles. We used a Cadbury's Hot Chocolate Can which has a 4"/10cm diameter. Cut circles with the can, combine the off cuts into a ball, knead and roll out again. This process always easier with 2 people. One rolling, one cutting, then making manti together.
There are many ways to shape manti, here are my 2 favorites. Put about a generous tablespoon of meat mixture into the circle piece of dough, careful for the meat not to touch the sides of the dough or it won't stick shut. Pinch and close the opposite sides of the dough together (corner to corner) until you have a little pinched dough pocket. Place on a tray and put in the freezer until frozen solid. Put in ziploc bags until ready to steam (or you can eat them fresh as in the next step).
Put about a generous tablespoon of meat mixture into the circle piece of dough, careful not to touch the sides of the dough or it won't stick shut. Pinch the middle of the dough together in the centre. Pinch the adjacent sides together, meeting in the centre, pinching all edges of the dough closed. It's going to kind of look like a star shaped pillow. Place on a greased steamer disks, about ½" apart from each other. Some use butter, but I generously sprayed oil.
Bring water in your mantavarka (steamer) to a boil. Place the steamer trays over the water and steam manti for about 30-40 minutes, until the meat is cooked.
Serve with Sour Cream and dill, or Lazadhzan, or with ketchup.