The watermelon is summer itself, read as refreshment, carefree joy and abundance shared among many. Cutting one open points to sharing feelings or plenty with others.
When this appeared in your dream, what were you feeling?
My Cosmic Code has a private dream journal. Write a dream down and the app picks out the symbols in it, shows what dream books say about them and, over time, which words recur across your entries. The journal is stored on your device only.