Heat oil in a large saucepan over medium heat until shimmering. Add onion and season with salt. Cook, stirring occasionally, until translucent. Add garlic and continue to cook 2 minutes more. Add tomatoes, season again with salt and bring to a boil. Reduce heat to a simmer and cover. Cook for 10 minutes. Uncover and continue simmering until onions are tender and sauce has thickened slightly, about 20-30 minutes. Taste and add more salt if desired.

Meanwhile, bring a large pot of heavily salted water to a boil. Once boiling add pasta and cook according to package instructions.

Place eggplant in a colander and generously season with salt. Toss to distribute salt and let drain in the kitchen sink while oil is heating.

Fill a large frying pan with 1/2-inch of olive oil and place over medium heat. Let heat until shimmering, about 5 minutes. Oil is hot enough when a piece of eggplant is immediately covered with bubbles when dropped in the oil.

Fry eggplant in two batches until golden brown, about 5 minutes, stirring occasionally. Remove to a paper towel-lined plate with a slotted spoon or bamboo skimmer and repeat with remaining eggplant.

Drain pasta and return to pot. Ladle tomato sauce over pasta (you may have leftovers depending on how saucy you like your pasta) and add fried eggplant. Gently toss to combine and serve with torn basil leaves.