In a large heavy skillet, heat 1 Tbsp. of the oil over medium heat.
Fry the onions in the oil until they are fragrant and tender.
Meanwhile, cook the rigatoni according to the package directions.
Add the eggplant to the skillet and drizzle it with the remaining oil and the salt, then add the tomatoes and bring it to a simmer (there will be enough liquid as the tomatoes begin to break down from the heat.)
Cover the pan and steam the vegetables for about 5 minutes until the eggplant begins to darken.
Remove the lid and add the herbs and tomato paste.
Simmer the sauce, stirring occasionally, for 15 – 20 minutes until the eggplant is very tender.
Stir in the capers.
Combine the sauce and pasta and serve it immediately or refrigerate the sauce for up to 3 days, or freeze it for up to 3 months.