Press the Sauté key on the Instant Pot (it should say Normal, 30 mins). Add the butter (or olive oil), onions, celery, salt and pepper and sauté for 4-5 minutes, stirring a few times.Add the rice, peas, garlic, stock and lemon zest and stir through. Press Keep Warm/Cancel key on the Instant Pot to stop the Sauté function. Make sure to scrape any rice kernels or vegetables off the inner pot walls.Place and lock the lid, making sure the steam releasing handle is pointing to Sealing. Press Manual, High pressure and set to 5 minute. After 3 beeps the pressure cooker will start going.Once the timer goes off, allow the pressure to release for 4-5 minutes and then, carefully, use the quick release method to release the rest of the steam and pressure.Open the lid and stir in the Parmesan cheese and drizzle with lemon juice. Serve while hot with a side salad or veggies.