Heat the olive oil in a medium skillet over medium heat. Add the shallot and sauté until soft, about 1 minute.

Add the mushrooms with a generous pinch of salt, sauté until soft and browned, about 6 to 9 minutes.

Stir in the tamari, balsamic vinegar, and mirin. Reduce the heat, then add the minced garlic, smoked paprika, and sriracha. Set aside to cool slightly.

In a food processor, combine the sautéed mixture, walnuts, flaxseed, brown rice, and ½ cup of panko. Pulse until combined but slightly chunky.

Transfer to a large bowl and fold in the remaining panko.

Form mixture into 8 patties, place them on a plate, and chill in the fridge for 1 hour.

If grilling, preheat a grill to medium-high heat. Brush the patties with olive oil, spray the grill with cooking spray, then place the patties on the grill. Press down lightly with a spatula. Grill about 7 minutes on one side, flip, and grill another 6 to 7 minutes until nicely charred.

Alternatively, cook them on the stove in a preheated cast-iron skillet over medium heat. Add oil and cook 5 to 6 minutes per side, or until well-charred.

Once cooked, remove from heat, brush with Worcestershire sauce, and serve with toppings.