The trick to swap calculations is understanding what your profit is. Profit is (what you receive - what you pay). You can use this to calculate swaps on interest rates, equity swaps, and so on.
What will you receive? You are receiving: CPI appreciation x Notional. (300/236 - 1) * 100,000 = 27,118.
What are you paying? You are paying the zero coupon rate. Let's say it is 10%, which is 10,000.
Final payoff to swap long at maturity = 27,118 - 10,000 = 17,118. You said "you have" the swap, so I assume you are the fixed rate payer.
In Excel, you could do something like this:
Modify for you specific swap.