Cut the eggplant into 2cm cubes, place in a colander set over a bowl, and toss with 1 tsp salt. Let drain 20 minutes, then pat dry with a clean towel.

While the eggplant drains, cut the potatoes, zucchini, peppers, celery, onion, and tomatoes into similarly sized pieces so everything cooks evenly.

Heat 3 tbsp of the olive oil in a 5-quart / 4.7L Dutch oven over medium heat. Add the onion and celery and cook 5 to 6 minutes, stirring, until soft and translucent.

Add the garlic and cook for 1 minute until fragrant.

Add the potatoes and cook for 5 minutes, stirring occasionally, until the edges start to soften.

Add the drained eggplant, zucchini, bell peppers, and the remaining olive oil. Season with salt, black pepper, and red pepper flakes if using, and stir to coat.

Add the tomatoes and the water or broth. Bring to a gentle simmer, cover, reduce the heat to low, and cook for 25 to 30 minutes, stirring every 10 minutes, until the potatoes are fork-tender and the vegetables have softened but still hold their shape.

Uncover and simmer 5 to 8 minutes more if the stew looks thin, letting the liquid reduce until it coats the back of a spoon.

Remove from the heat, stir in the torn basil, and taste for salt. Serve warm, or let cool and serve at room temperature.