In a mixing bowl, combine flour and salt. Slowly add water to knead into a smooth and soft dough. Cover the dough with a damp cloth and let it rest for 20-30 minutes.
Heat butter or oil in a pan. Add chopped onions and sauté until soft. Add boiled corn kernels and cook for a minute or two. Season with salt, pepper, and oregano (if using). Allow the mixture to cool slightly.
Once the corn mixture has cooled, mix in the grated cheese. Stir well until the cheese melts and blends with the corn.
After the dough has rested, divide it into small equal-sized balls (about 12-15 balls). Roll each ball into a small circle, about 3-4 inches in diameter, using a rolling pin.
Place a spoonful of the corn and cheese mixture in the center of each dough circle. Be careful not to overfill.
Pinch the edges of the dough together and pleat them to seal the momo. You can make different shapes—either half-moon or round, depending on your preference.
Grease a steaming tray or use parchment paper to prevent sticking. Place the momos in a steamer, leaving space between each. Steam for 10-15 minutes or until the dough is fully cooked and the momos are soft.
Serve the hot corn and cheese momos with a dipping sauce (chili sauce or soy sauce) or chutney.