Cook the penne in a pot of boiling salted water. Stir to prevent the pasta from sticking together. While the pasta is cooking, make the sauce.
To make the sauce: In a saucepan, heat up 4 tablespoons of olive oil. Gently saute the chopped onions until tender, then add the plum tomatoes and liquid from the can. With the back of a wooden spoon, break up the tomatoes into little chunks. Season the sauce with salt, and pepper, to taste. Cook the tomato sauce for a few minutes, until the sauce has thickened.
In another pan, heat olive oil and fry the eggplant cubes until golden.
Drain the eggplant cubes on a paper towel to remove the excess oil. Drain the pasta approximately 2 minutes before the 'al dente' stage and add the pasta to the saucepan. Finish cooking the pasta in the sauce. Add the fried eggplant, basil leaves and sprinkle with ricotta salata. Mix the ingredients together well in the saucepan so that the pasta and the sauce are well amalgamated or combined. Be careful not to overcook the pasta. Transfer the pasta to a warm serving bowl or divide the pasta among warm plates and sprinkle extra ricotta salata on top and serve immediately.