Put flour and sesame seeds on separate sheets of wax paper and in a shallow bowl beat together egg white and water.
Season chicken breasts with salt and dip them, 1 at a time, in flour, shaking off excess. Dip chicken in egg white, letting excess drip off. Then coat with sesame seeds on 1 side, shaking off excess. Transfer chicken breasts as coated to a plate.
In a large nonstick skillet heat 1 teaspoon oil over moderate heat until hot but not smoking and cook chicken, sesameseed sides down, until golden, about 4 minutes. Turn chicken and cook 4 minutes more, or until just cooked through. Add lemon juice to skillet. Turn chicken to coat with juice and cook until juice is almost evaporated, about 1 minute. Transfer chicken to a cutting board and halve lengthwise.
Make a horizontal cut through center of each baguette piece with a serrated knife, cutting almost but not all the way through, and spread open. In a bowl toss together cabbage, spinach, carrot, remaining teaspoon oil, and salt to taste.
Make sandwiches with slaw, chicken, and bread, pressing together gently.