Heat 3 tablespoons olive oil in a 12-inch skillet over medium-high heat.

Add the diced eggplant and a pinch of salt to the skillet.

Cook, shaking and tossing occasionally, for 10-11 minutes, or until the eggplant is brown and softened. Reduce heat if necessary to prevent burning.

Transfer the cooked eggplant to a bowl, cover with foil, and set aside.

Add the remaining 1/2 tablespoon olive oil to the skillet and increase the heat to medium-high.

Add the chopped onion and a pinch of salt.

Cook, stirring frequently, for about 3 minutes, until the onion is softened.

Add the minced garlic and red chili flakes.

Cook for about 30 seconds, until fragrant.

Add the canned whole peeled tomatoes and their juice to the skillet.

Bring to a simmer.

Once the tomatoes have softened, gently break them apart with a potato masher.

Cook the sauce until thickened, seasoning to taste, for 8-10 minutes.

Add the chicken stock or water and bring to a gentle simmer.

Add the uncooked penne pasta to the sauce and cover the skillet.

Cook over medium heat, making sure there are active bubbles, stirring occasionally to prevent sticking.

Cook the pasta until firm to the bite, about 12-15 minutes.

Stir in the cooked eggplant.

Tear the fresh mozzarella into small chunks and add to the pan.

Heat until the mozzarella is just starting to melt, about 1 minute.

Stir in the roughly chopped basil.

Season to taste with salt and pepper.

Serve immediately.