In the cantaloupe type melons, if they split you for sure waited too long to harvest them.
I don't really know anything about growing watermelon or pumpkin.
Have you tried any of the Asian Cucumbers? They may look odd compared to the supermarket types we are more used to seeing but they are really good, super productive and can take the heat.
If you like green beans (snap beans what we used to call string beans) I really, really urge you to grow yardlong beans. Thrive in the heat as they are from tropical Southeast Asia.
