Dubia Roaches need a high protein food provided to them at all times. There are two things you can do, Buy a Dubia roach chow online or make your own.
If you want to buy online then just google for dubia roach chow and order it. The roach guy offers a great roach chow.
If your going to make your own then here is how you can do it. A lot of people use dog food as a high protein mix for their dubia roaches mixed with oatmeal, wheat, or oats. And make sure you provide fresh fruit and vegetables every couple of days. You can also use cat food or even ferrett food as a protein source. Also, here are some more things you can use to mix with your protein source; Cereal, fish food, grape nut flakes, powdered milk, organic oats, and oatmeal. Throw what you have decided to use into a coffee grinder or another grinder and feed it to your dubia roach colony. Now remember again to throw in fresh fruit and vegetables every couple of days or so into your dubia roach colony.