Heat Olive Oil In A Large Skillet Over Medium Heat. Add Onion, Celery, Carrot, Green Pepper, And Garlic: Saute Until Tender. Stir In Tomatoes, Chili Powder, Tomato Paste, Vinegar, And Pepper. Cover, Reduce Heat, And Simmer 10 Minutes. Stir In Kidney Beans, And Cook An Additional 5 Minutes. Cut A 1/4 Inch Slice Off The Top Of Each Kaiser Roll; Set Aside. Hollow Out The Center Of Each Roll, Leaving About 1/2 Inch Thick Shells; Reserve The Inside Of Rolls For Other Uses. Spoon Bean Mixture Evenly Into Rolls And Replace Tops. Serve Immediately.