Place eggplant cubes in colander, sprinkle generously with salt. Let stand for 30 minutes. Rinse and drain thoroughly.
Cook ziti in large amounts of boiling salted water until tender; drain. Add butter and toss to coat.
In large skillet, cook eggplant, onion and garlic in oil until tender. Stir in tomatoes and tomato paste, 1/2 tsp salt, basil, oregano and red pepper flakes. Bring to a boil. Reduce heat and simmer 15 minutes, stirring occasionally. Remove from heat and stir in parmesan cheese.
In small bowl, blend ricotta cheese, egg and remaining 1/2 tsp salt.
In shallow three quart (3mL) casserole, layer half each: cooked pasta, tomato mixture, ricotta cheese mixture and mozzarella cheese. Repeat layering with remaining ingredients. Bake at 350 for 45 minutes or until cheese melts.