Preheat oven to 400° F.

Trim eggplant and slice into 1/2” pieces. Sprinkle both sides of each slice with salt and let sit for 10 minutes (this helps remove moisture from the eggplant before cooking), then blot off any extra moisture with a paper towel.

Coat bottom of a large skillet with oil (about 3 tablespoons) and place over medium heat. When the oil is hot, carefully add the eggplant. Cook until bottoms are golden, about 5 minutes, then flip slices and cook until bottoms are golden, about 9-10 minutes total.. Remove slices to a paper towel-lined plate to drain off any excess oil. Return pan to the heat.

If there is no more oil left in the pan, add 1 tbsp of oil along with the onion and garlic over low to medium heat for 3-4 minutes or until onions start to soften. Add the tomatoes, season to taste and add the red pepper flakes (if using). Bring just to a boil, then reduce to a simmer and cook for 10 minutes.

When the sauce is ready, make a layer of eggplant at the bottom of a baking dish, followed by a layer of tomato sauce, then cheese, then eggplant, tomato sauce, cheese. Place in oven and bake for 12 minutes or until the cheese is melted and bubbly. Garnish with basil if desired.