Fastest way I found was to downgrade the row 2 catapult to level 1, then finish the level and replay, it will start you with what you left with. Now plant 6 tomatoes, move row 2 and row 4 catapult to the almost front the second white square and throw tomotaes as fast as you can, you can alternate catapults to make it faster. I needed to plant 6 extra tomatos for row 2 and move the catapult, so it may take some adjustment, but all you need to do is break through the top of the hut then hit the tnt, if you have trouble hitting the tnt, move the catapult a touch forward.