Prep the binder: In a small bowl, mix ground flaxseed with 2 1/2 tablespoons water. Let it sit 5–10 minutes to gel. If using an egg, skip this step.

Grate the beet: Peel and grate the beet on the large holes of a box grater. Pat lightly with a paper towel to remove excess moisture, but don’t squeeze it dry.

Mash the beans: In a large bowl, mash the chickpeas or black beans with a fork or potato masher until mostly smooth with some small chunks for texture.

Build the mixture: Add the grated beet, onion, garlic, oats, breadcrumbs, cumin, smoked paprika, coriander (if using), salt, and pepper to the beans. Stir in the flax “egg,” lemon juice, and olive oil.

Adjust texture: The mixture should be moist but not sticky. If it clings to your hands, add 1–2 tablespoons more oats or breadcrumbs. If crumbly, splash in 1–2 teaspoons water or an extra drizzle of oil.

Shape patties: Divide into 4 large or 6 smaller patties, about 1/2 inch thick. Press the edges to compact so they hold their shape.

Preheat the air fryer: Set to 375°F (190°C) for 3 minutes. Lightly brush or spray the basket with oil to prevent sticking.

Air fry the first side: Place patties in a single layer without crowding. Brush the tops with a thin coat of oil. Cook 8–10 minutes until they firm up and darken slightly.

Flip and finish: Carefully flip and cook another 6–8 minutes. They’re done when the edges are crisp and the centers feel set. Total time varies by thickness and air fryer model.

Warm the buns: Toss buns into the air fryer for the last 1–2 minutes to toast lightly.

Assemble and serve: Spread sauce on buns, add patties, and stack with your favorite toppings. Taste and add a pinch of salt if needed.