Preheat the oven to 350F and lightly oil a 9x13" rectangle pan.
Trim and cut the eggplant into 1-inch cubes. Place it into a colander. Sprinkle it generously with salt, then allow it to sit for 25 minutes. Rinse the eggplant well, then pat it dry firmly.
Bring a large pot of salted water to boil and cook the pasta according to package instructions, till it's al dente. Drain.
While the pasta cooks, heat the olive oil in a large deep skillet over medium high heat. Add the eggplant. Allow it to sizzle for 4-5 minutes, until it's just starting to brown. Reduce the heat to medium low. Continue cooking the eggplant for 8 (or so) more minutes, until it's meltingly tender. If it's not cooking quickly enough, try covering the skillet for a minute or two.
When the eggplant is cooked, add the pasta and marinara sauce to the skillet. Mix and heat everything through.
Layer a third of the pasta mixture into your rectangle pan. Dot this with a third of the ricotta, using a knife to spread the ricotta around a bit. Cover this with another third of the pasta and ricotta. Finish with a layer of pasta and lightly dot the top with the remaining ricotta. Transfer the casserole to the oven and bake for 30-35 minutes, or until hot and bubbly. Serve.