In a medium saucepan, combine two cups of water, carrots, lentils and ¼ teaspoon salt. Bring to a boil. Reduce heat to low, cover saucepan and simmer until lentils are tender, about 12 to 14 minutes. Drain in a colander and let cool for 20 minutes.
Toast cashews over medium-low heat, stirring frequently for two to four minutes or until golden and fragrant. Let cool.
Heat two tablespoons of oil in a large skillet over medium heat. Add onion and cook until softened, five to eight minutes. Add garlic, curry powder, and two tablespoons of water and cook for an additional minute, stirring frequently. Remove from heat and let cool.
Pulse the cashews in a food processor or blender. Add lentils and onion mixture and pulse. The mixture should be cohesive, but still textured. Transfer to a large bowl, stir in breadcrumbs and mix well. Add salt and pepper to taste.
Form the mixture into one-inch thick patties (it should make about six). Cook patties in a large skillet over medium heat until golden brown, roughly four minutes per side. Serve burgers in whole-wheat pitas with lettuce, cucumber, mayo or cucumber-mint raita, if desired.