Dice the onion and mince the garlic. Add the onion, garlic, and olive oil to a large pot. Sauté over medium heat until the onions have softened.
While the onion and garlic are cooking, dice the eggplant into ½-inch pieces. Add the eggplant to the pot with the Italian seasoning, salt, and pepper, and continue to sauté over medium heat.
Dice the red bell pepper. Once the eggplant has softened, add the diced bell pepper to the pot and continue to sauté.
Slice the zucchini into ¼-inch thick quarter-rounds, then add them to the pot. Continue to sauté just a couple minutes more, or until the zucchini just begin to soften.
Add the red sauce and 1/4 cup water to the pot and stir to combine. Let the vegetables simmer in the sauce for 5-10 minutes, or until they reach your desired level of tenderness.
While the vegetables are simmering, bring a separate pot of water to a boil.
Once boiling, stir in the salt, then pour in the cornmeal while whisking. Continue to cook and whisk until the cornmeal thickens (this should happen quickly).
Once the cornmeal has thickened, stir in the butter until melted, then add the grated Parmesan. Stir to combine, then taste and adjust the seasoning to your liking.
To serve, spoon ⅔ cup cornmeal into a bowl then top with one cup of the vegetables and red sauce. Garnish with chopped parsley if desired.