Mix ground flaxseed with 3 tablespoons water in a small bowl and let sit for 5 minutes to thicken.
In a large bowl, combine the flax mixture, black beans, grated beetroot, diced onion, crushed garlic, frozen sweetcorn, coriander powder, thyme, smoked paprika, flour, and soy sauce. Mix well until combined.
Using your hands, form the mixture into 4 equal patties, pressing firmly to help them hold together.
Heat oil in a large skillet over medium heat.
Fry the patties for 4-5 minutes per side until crispy on the outside and cooked through.
Serve on burger buns with your preferred toppings.