Preheat your oven to to 400°F and line a baking sheet with parchment paper.
Whisk together the glaze ingredients in a small pan over medium heat. Cook, stirring frequently, until the glaze thickens slightly. If it becomes too thick, you can add a little water to thin it down.
Place the oats in a food processor and pulse until resemble a coarse flour. Add the rice, black beans, chickpea flour, and scallion to the food processor along with ¼ cup of the teriyaki glaze and pulse until the mixture resembles a thick paste.
Form the mixture into four patties and place them on the baking sheet. Brush on about half of the glaze and bake for 20 minutes. Flip the burgers, brush on the remaining glaze, and bake for another 5 to 10 minutes, until golden brown and firm.
While the burgers are cooking, heat the oil in a grill pan or large skillet over medium high heat. Place the onion and pineapple rings in the pan and cook for approximately 5 minutes on each side. If you’re using a grill pan, you’ll want nicely browned grill lines. If you’re using a skillet, cook until the onions and pineapple slices are golden on each side. If you have an outdoor grill, you can use it to cook the onions and pineapple
Serve the burgers on the buns along with the grilled onions and pineapple slices. Top with lettuce, tomato, and spicy mayo, if using.