Stir together flour, 1/2 teaspoon salt, and 1/4 teaspoon black pepper in a small bowl until combined; sprinkle over steak. Pound flour mixture into meat with a mallet or the edge of a sturdy plate.

Heat oil in a large skillet over medium heat. Cook floured steak in hot oil until browned on both sides, about 15 minutes. Reduce heat to low and pour in water. Cover the skillet and simmer until meat is tender, about 1 hour. Add more water to the skillet if needed to prevent burning.

Mix together tomatoes, green bell pepper, onion powder, remaining 1/2 teaspoon salt, and 1/8 teaspoon black pepper in a medium bowl until combined; pour over steak in the skillet. Bring to a simmer and cook until sauce has thickened, about 30 minutes.