Drain and rinse the canned black beans well. Transfer to a large bowl and gently mash about two-thirds of the beans with a fork or potato masher, leaving some whole beans for texture.

Sauté aromatics

Heat 1 tablespoon olive oil in a small skillet over medium heat. Add the diced onion and cook 4–5 minutes until softened and just beginning to brown. Add 2 teaspoons minced garlic and cook 30 seconds until fragrant. Remove from heat and let cool 2 minutes.

Mix patty base

Add the cooked onion and garlic, rolled oats, ground cumin, smoked paprika, black pepper, salt, lime zest, lime juice, and chopped cilantro (if using) to the mashed beans. Mix thoroughly until the mixture holds together when pressed. If too wet, add up to 2 tablespoons more oats; if too dry, add 1–2 teaspoons water or a splash more lime juice.

Form patties

Divide the mixture into 4 equal portions (about 3/4 cup each) and shape into compact patties about 3.5 inches (9 cm) wide and 1/2 inch thick. Press the edges so they hold together.

Cook patties

Warm remaining 1 tablespoon olive oil in a large nonstick skillet over medium heat. Add patties (work in batches if needed) and cook 4–5 minutes per side until a crisp dark brown crust forms and patties are heated through. Flip gently to avoid breaking. Alternatively, bake on a parchment-lined sheet at 200°C (400°F) for 12–15 minutes, flipping halfway.

Kachumber

Combine the diced cucumber, tomato, finely diced red onion, chopped cilantro, 1 tablespoon lime juice, 1/2 teaspoon salt, and 1/4 teaspoon chili powder in a bowl. Toss gently and taste; adjust salt or lime as needed. Let rest 5–10 minutes to marry flavors.

Vegan Garlic-Lime Sauce

Whisk together vegan mayonnaise, vegan yogurt, 2 teaspoons minced garlic, 1 tablespoon lime juice, 1/2 teaspoon lime zest, 1/2 teaspoon salt, 1/4 teaspoon black pepper and 1/2 teaspoon maple syrup in a small bowl until smooth. Taste and adjust seasoning. Chill in fridge at least 10 minutes to let flavors meld.

Chutney

Stir the chopped cilantro into the mango or tomato chutney. If chutney is very thick, thin slightly with 1–2 teaspoons water or lime juice to a spreadable consistency.

Assembly & Serving

Heat a small skillet over medium-low and add 1 tablespoon neutral oil or vegan butter. Split the pretzel buns and toast cut-side down 1–2 minutes until golden and slightly crisp.

Spread about 1 tablespoon of the garlic-lime sauce on the bottom bun and 1 tablespoon of chutney on the top bun.

Place a lettuce leaf on the bottom bun, add a cooked black-bean patty, top with 2–3 tablespoons kachumber, a slice or 2 of tomato and a little sliced red onion if using.

Finish with the chutney-smeared top bun. Serve immediately with extra sauce and chutney on the side.