1. Cut each chicken breast in half. Discard peripheral fat and membranes. 2. Core the tomatoes and cut them into 1/2-in cubes. There should be about 2 1/2 c. loosely packed. 3. Peel the cucumbers and trim off the ends. Cut the cucumbers into 1 1/2-in lenghts and quarter the pieces lenghtwise. Discard nthe seeds. There should be about 3 c. loosely packed. Season with salt and pepper. 4. Heat the oil in a large, heavy skillet and add the chicken breasts in one layer. Cook over moderately high heat, shaking the pan nand lifting the pieces, about 2 min. or until golden brown. Turn the pieces and cook 3 min. on the other side. Transfer to a warmed dish and keep hot. 5. Add the onion and the garlic to the skillet and cook, stirring, for 1 min. Add the tomatoes and stir. Cook 1 min., then add the wine and broth. Stir to blend and cook 1 min. more. 6. Add the cucumber pieces and any liguid that has accumulated around the chicken pieces on the plate. Add salt and pepper to taste. Cook over high heat about 6 min. 7. Return the chicken to the skillet and turn to coat with the sauce. Add the saffron. Cover the skillet and cook 4 min. Then serve.