Spray a springform pan with cooking spray and set aside.
In a medium size pot, melt 1 tbsp of butter on medium low heat.
When the butter is melted add 1.5 cups of mini marshmallows. Stir the marshmallows and they will begin to melt.
As they begin to lose their shape and melt stir in the green food coloring and remove from heat.
Stir in 2 cups of rice krispie cereal and combine well.
Drop the now green rice krispie treats into the springform pan. Using a piece of parchment paper, push it to the outer edge of the pan to create the "rind".
In another pot repeat the process using the remaining ingredients(2 tbsps butter, 2.5 cups marshmallows, 3 rice cereal).
At the marshmallows stage instead of adding green food coloring, add the pink.
Place the mixture in the middle and push it down with parchment paper to create the inside of the watermelon.
When it is slightly cooled, gently push in the mini chocolate chips to be the seeds.
Let the whole pan cool and cut into slices when it is at room temperature.