Heat 2 tablespoons olive oil in dutch oven over medium heat.
Next, add diced onion and garlic into the dutch oven and sauté for 2-3 minutes until fragrant and onions are slightly translucent.
Add in crushed tomato, herbs, salt, pepper, crushed red pepper, and sugar. Stir until sauce begins to simmer then lower temperature to low heat and allow to cook until slightly reduced.
While the sauce is cooking, in a frying pan, heat the canola oil to a medium-high temperature.
Once the oil is hot, cook the sliced eggplant in batches, being careful not to crowd the pan. Remove the eggplant slices as soon as they begin to brown, placing them on a paper towel to drain excess oil. Repeat this step with the potato slices.
Remove the sauce from the heat and allow to cool slightly. Next, arrange the sliced vegetables into the bottom of the pot - alternate between the potato, zucchini, squash, eggplant, and tomato slices. Arrange into spiral shape.
Cover and place the dutch oven back on the burner on medium to low heat for about 20 minutes. Then remove remove lid and allow the vegetables to continue simmering for another 20 minutes while the excess water evaporates.
Serve with rice or crusty French bread.