This is counterintuitive but to make cooked cauliflower rice have a thicker clumpy texture like cooked regular rice you should actually cut it more finely. I like the food processor for this. If you cut the cauliflower into more coarse grains they will not stick together. Also, it is key to use just a little liquid with the freshly chopped riced cauliflower to get it to clump up and thicken. This softens the cauliflower. Note that it is hard to thicken frozen cauliflower rice as it is usually larger "grains" so it is important not to add too much excess moisture to it.