Beware of ANY dry dog, cat, ferret, etc. foods as gut-load for feeders. The meat by-products used in them is not pasteurized and can cause serious bacterial infections in your geckos. Stick with human-grade cereal products and frosh produce, avoiding spinach as it is a calcium binder.
For the protein you can use fish food flakes, Its safe and I have lately avoided most cat and dog dry for rhe roaches and any other feeder. Although I raise Manx cats and have three dogs I was so darn lucky(so far) that the food I use wasn't recalled and I use one of the very best foods, organic ect. OH and if you use any kale you must have other greens with it and very little kale But no spinach. I use a spring mix and field greens then add mustard greens and turnip greens to the mix and some times collard greens because I also have Leopard Tortoises and Bearded Dragons and know all about the calcium binding and phospherous/ calcium mixes. Good Luck, Deb