WOW! You are VERY lucky! CONGRATULATIONS!
The Seasonal Attack Pea is one of the strongest weapons in the game. Dealing a WHOPPING 28 SOLID icons! A mix of Light and Earth. For comparison, a Super Attack pea, the strongest constant in the game, deals 32 solid icons.
LOL It's no wonder you are one-shotting most of your opponents with a weapon like that in your arsenal!
I'd love to win one too, there's still MOST of the Advent Calendar Days left, so I have hope!
So, just battle as efficiently as you usually would. You could use your SAP and your Grenade along with Lens Flare for your first turn, and if you still haven't defeated your opponent then, then just do your second turn like you normally would. Maximize the damage you deal while minimizing the damage you take. Since the SAP is multiple use, you can use it in round 2 as well, with your 2nd strongest weapon you'll wipe the floor with most opponents! lol You should have a MUCH easier time with even stronger opponents than the ones you listed too.
I hope that answers your question. If you've any others, feel free to ask! And Congrats again!