Start by thoroughly washing and chopping the zucchini, bell peppers, onion, and garlic into small, even pieces.

Turn on the Instant Pot and select the sauté function. Add a splash of oil, and once it’s hot, toss in the chopped onions and garlic.

Pour in the tomato sauce and sprinkle your Italian seasoning over the sautéed vegetables.

Secure the lid on your Instant Pot and set it to cook on high pressure for 10 minutes.

Open the lid and give your casserole a good stir. Sprinkle in the cheddar cheese, allowing it to melt.

After mixing well, your casserole is ready to serve! Ensure everything is well combined, and ladle generous portions onto plates.