Preheat oven to 350. Spray a 13×9 inch baking dish with non-stick cooking spray.
Heat olive oil in a large skillet. Add leeks and cook until tender.
Add cannelini beans, season with salt and pepper. Mix in a half jar of sauce. Remove from heat.
Cook polenta according to package directions.
Spoon half the cooked polenta into a 9×13 inch baking dish. Spoon beans over polenta. Sprinkle half the shredded cheese over beans. Cover with remaining polenta and sprinkle with remaining cheese.
Bake at 350° for 20 minutes. Heat remaining sauce and serve over polenta.