Directions

1. Stir water and flaxseed meal together in a small bowl until well combined; let stand until thickened, about 5 minutes.
2. Meanwhile, peel onion and cut in half lengthwise. Chop half of the onion (you'll have about 1/2 cup chopped). Slice the remaining half into half-moon slices (you'll have about 1/2 cup sliced). Heat 1 tablespoon oil in a large nonstick skillet over medium heat. Add mustard seeds; cook, stirring occasionally, until fragrant and beginning to pop, 1 to 2 minutes. Add the chopped onion, garlic, ginger and chile; cook, stirring often, until starting to soften, about 3 minutes. Stir in garam masala, turmeric and salt; cook, stirring constantly, until fragrant, about 30 seconds. Remove from heat.
3. Pulse oats in a food processor until ground into a rough meal, about 10 pulses. Add chickpeas, cilantro, carrots, cashews and the mustard seed-onion mixture. Pulse until well combined and beginning to pull away from the sides of the bowl, about 10 pulses, stopping to scrape down sides as needed. Add the flaxseed mixture; pulse until combined, 2 to 4 pulses. Transfer to a large bowl. Divide into 4 portions (about 1/2 cup each); shape each portion into a 4-inch patty (about 1/2 inch thick).
4. Wipe the skillet clean. Add the remaining 2 tablespoons oil; heat over medium heat. Add the patties; cook until golden and crisp on both sides, about 4 minutes per side.
5. If desired, spread vegan mayonnaise evenly over split bun halves. Place 3 lettuce leaves and 2 tomato slices on each bottom bun and place 1 patty on top. Top with the sliced onion. Garnish with additional cilantro, if desired. Replace top buns and serve.