Cook pasta in a large pot of boiling salted water until al dente, according to package instructions. Drain pasta; return to pot.
Heat oil in a large skillet over medium heat. Add onion, garlic, and crushed red pepper; cook, stirring, until softened, about 5 minutes.
Add eggplant to skillet; season generously with salt and pepper. Cover, and cook until eggplant begins to release juices, about 5 minutes. Uncover; cook, stirring, until tender, 3 to 4 minutes (if bottom of pan browns too much, add a few tablespoons water, and scrape with spoon).
Add tomatoes, tomato paste, and 1/4 cup water to skillet; cook, stirring, until softened, about 5 minutes.
Toss sauce and basil with pasta; gently reheat if necessary. Top each serving with a spoonful of ricotta, and garnish with more basil.
Crushed red pepper adds spice to this dish. Vary the amount according to taste.