Place the carrots, onion and garlic into a food processor bowl. Pulse until finely chopped, stopping to scrape down sides of bowl as needed.
Add the panko breadcrumbs, walnuts, cilantro, cornstarch, flax seeds, lime juice, cumin and salt. Blend until completely mixed, stopping to scrape down sides of bowl as needed. Add a splash of water if the mixture seems a little dry.
Shape mixture into 3 patties. (see Note)
Coat a large skillet with olive oil and place it over medium heat.
Working in batches if necessary, place the burger patties in skillet and cover. Cook about 4 minutes, until lightly browned on bottoms. Gently flip, cover the skillet again, and cook another 4 minutes on opposite side.
Whisk all ingredients together in small bowl.
Place a burger inside each bun. Top with spicy maple ketchup and greens.
