No. – Watermelon is not allowed on the slow carb diet, except on your Cheat day.
Fruits, in general are not allowed on the slow carb diet, except on your Cheat day, with the exception of:
Avocados (up to 1 cup/day) and Tomatoes.
On your Cheat day, organic Grapefruit Juice and Lemon Juice are recommended for the maintenance of blood sugar, and prevention of insulin spikes.