Preheat oven to 250°F and line a 9" × 13" baking dish with parchment paper.
Add oats and pecans in a food processor. Pulse until a coarse flour forms. Add in 1 can black beans, rice, ground flaxseed, nutritional yeast flakes, dehydrated onions, garlic powder, salt, and chili powder. Pulse 3 seconds, then use a spatula to push ingredients down. Pulse again 3 seconds. Add second can black beans and pulse again to combine. Mixture should be a spreadable consistency.
Spray a large skillet with vegetable spray and place over medium heat. Form bean mixture into 8 patties and place 3–4 patties in skillet. Cook 6 minutes on each side.
Place patties in baking dish and bake 10 minutes. Set cooked patties aside and repeat process with remaining patties. Once done, let patties cool about 5 minutes.
Place burgers in a large sealed container and refrigerate up to 7 days, or freeze up to 2 months. To serve, cook patties in microwave in 30-second intervals until heated through. Serve on buns.