In a small bowl, combine mayonnaise and chili powder and set aside.
Heat a large skillet over medium-high heat and pour in the olive oil. Sprinkle the steak on all sides with 1/8 teaspoon of salt and 1/4 teaspoon of black pepper. Place steak in preheated skillet and fry for about 15 minutes, turning once. Transfer the steak to a cutting board and rest.
Put the onion in the same frying pan, pour 1 tablespoon of water and add about 1/8 teaspoon of salt. Reduce heat to medium-low and cook onion for 5-7 minutes, until soft.
Meanwhile, in a separate bowl, combine cucumber, ginger, lemon juice and 1/8 teaspoon of salt and stir.
Cut the steak into thin slices across the drag. Put the mayonnaise mixture on the ciabatta slices, and top with the chopped meat and onions. Serve the cucumber salad with the meat sandwiches.