1. Preheat the oven to 350°F (177°C). Line a sheet pan with parchment paper.
2. Add the rice, 1 cup (240g) water, and 1⁄4 teaspoon salt to a medium pot and stir. Bring to a boil, cover, reduce the heat to low, and simmer for 30 to 35 minutes or until all the water is gone. Remove from the heat (keep covered), and let it steam for 5 minutes. Fluff with a fork and leave uncovered for 15 minutes to cool.
3. Meanwhile, add the onion and 3 tablespoons (45g) water to a pan over medium-low heat. Bring to a simmer, cook 5 minutes, stirring occasionally, until the onions are tender. Once the water is gone, stir the onions constantly for a couple of minutes to brown them. Add the onions to a food processor, along with the teriyaki sauce, sesame seeds, garlic powder, black pepper, and, if desired, red pepper flakes. Pulse to combine the spices with the sauce and break up the onions a bit, but not puree them. Add the chickpeas and pulse several times to break up the chickpeas into tiny pieces, but do not puree them. Add the cooled rice, rice flour, and oats, and pulse several times until it all comes together into sticky chunks. You want the mixture to hold together but do not want to overmix it.
4. Transfer the mixture to a bowl. Use a 1⁄2-cup measuring cup to scoop out the chickpea mixture, pressing it into the cup to flatten it. Plop the patty out into your hand, shape into a ball, and place on the prepared pan. Press down until the chickpea mixture is 1 inch thick, and shape the edges into a round patty. Repeat the procedure with the remaining chickpea mixture to get 6 patties total.
5. Bake at 350°F for 20 minutes, flip them over, and bake 10 more minutes. Let cool for 10 to 15 minutes. The patties firm up on the insides a lot as they cool.
6. To serve, I like to dress buns with lots of teriyaki sauce, lettuce, and extra sesame seeds, but choose whatever toppings you prefer. Store leftover patties in the fridge wrapped tightly in plastic wrap and placed in an airtight container. These reheat well in the microwave and also in the oven on low heat.
Salt, pepper and water are not included in the 8-ingredient count.