Chop and grate all vegetables finely to ensure even cooking.

If using black beans, mash them well with a fork or blender.

Cook the brown rice if not already prepared.

Heat a non-stick pan over medium heat with a little olive oil.

Add onions, bell peppers, carrots, celery, and mushrooms. Sauté for 3-5 minutes until they soften.

Stir in garlic powder, onion powder, paprika, black pepper, and salt. Cook for another 2 minutes, then remove from heat.

In a large mixing bowl, combine the sautéed vegetables, black beans (or soy granules), brown rice, and oats.

Add flaxseed meal (or egg), bread crumbs, soy sauce, and mustard/tomato paste.

Mix everything well until you get a sticky mixture that holds together.

Take a handful of the mixture and form it into a patty shape (about ½-inch thick).

Place the patties on a lined baking sheet or a plate.

Place the patties in the refrigerator for 30 minutes to firm up.

To pan-fry: Heat a non-stick skillet over medium heat and add 1-2 tablespoons of olive oil. Place the patties in the pan, ensuring they do not overlap. Cook for 4-5 minutes on one side until golden brown. Flip carefully and cook for another 4-5 minutes on the other side. Remove from heat and let rest for a minute before serving.

To bake: Preheat your oven to 375°F (190°C). Line a baking sheet with parchment paper or lightly grease it. Place the patties on the sheet, leaving space between each one. Bake for 20-25 minutes, flipping halfway through to ensure even cooking. Remove from the oven and let them cool for 5 minutes before serving.

To air-fry: Preheat your air fryer to 375°F (190°C). Lightly spray the air fryer basket with cooking spray. Place the patties inside the basket in a single layer. Air-fry for 12-15 minutes, flipping halfway through. Remove and let them cool before assembling your sandwich.