In a pot, combine 1 cup buckwheat, 1 cup water, and 1 teaspoon salt. Bring to a boil over medium-high heat, then reduce to medium and simmer for about 10 minutes until all water is absorbed.
Remove from heat and let cool for 2 minutes. Stir in 5 tablespoons flour, the finely diced onion, finely minced garlic to taste, and 1 tablespoon soy sauce. Mix and knead together until well combined.
Wet your hands with water. When the mixture is cool enough to handle, shape it into about 5 patties.
Heat 3 tablespoons oil in a large skillet over medium-high heat. Place patties in the hot oil and fry for 5-8 minutes until golden brown on one side, then flip and fry for another 5-8 minutes until golden brown on the other side. Transfer to a plate and serve.