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Add the walnuts to a food processor and pulse until it forms large crumbs.
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Heat a skillet over medium heat. Add the walnuts and toast 5-6 minutes until fragrant and lightly golden. Stir in the chili powder, cumin, paprika, oregano and salt. Cook another 1-2 minutes. Transfer to a medium bowl.
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Wipe the skillet and heat oil over medium heat. Add the onion and garlic and sauté until fragrant, about 5 minutes. Set aside.
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In the same food processor, add the kidney beans, tomato paste and soy sauce. Process until combined. Add the onion and garlic and pulse a few times. Transfer the mixture to the bowl with the walnuts.
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Stir in the flour into the mixture and mix until combined.
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Form 4 patties with the mixture using your hands. Lightly brush with oil.
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Heat the grill over medium heat or heat oil in a skillet over medium heat.
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Cook the patties for 4-5 minutes on each side.
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Serve in a hamburger bun with toppings of choice.