Dice potatoes into 1/2" pieces
Cut zucchini into 1" chunks.
Slice bell peppers.
Quarter and slice tomatoes.
In a large oven proof pan, saute onions, basil, and celery in olive oil.
Add tomatoes, zucchini, and potatoes.
Preheat your oven to 350.
Stir gently, then cover and steam until tender for about 10 minutes.
Remove the pan lid, add parmesan overall and place your pan into the oven for 10 minutes.
Remove the pan from your oven, and let cool for 5 minutes before serving. Enjoy!