Put zucchini and water in the Instant Pot. Close the lid and turn the valve to a Sealing position. Press the "Pressure Cook" or "Manual" button and set the time to 2 minutes on High pressure.
When it's done cooking, quick release (QR) the steam. Drain zucchini in a colander.
Add olive oil and minced garlic to the Instant Pot and press the Saute button. When the garlic starts sizzling (in about 1 minute), add drained zucchini, tomato sauce, salt, red pepper flakes and Italian seasoning, and mix until combined. Add salt to taste if needed. Cook for 2 minutes, then remove to a serving dish.