Prepare all the vegetables into medium to large-size dice. Add 2 tablespoons of olive oil to a large rondeau pot over high heat until it begins to smoke lightly.
Next, add in the eggplant, gently season with salt, and quickly sauté for 90 seconds, or just until 1 or 2 sides are browned. Set them aside on a plate in a single layer to cool slightly.
Pour in 1 tablespoon of olive oil to the pot and once it smokes, add in the zucchini gently season with salt, and sauté for 2 minutes or until 1 or 2 sides is browned.
Set it aside on a separate plate in a single layer to cool slightly. Add 1 more tablespoon of olive oil to the pot over medium heat and add in the onions. Gently season with salt and sauté.