Keep the pieces of cauliflower larger to get a crunchy “exoskeleton” without the whole piece getting cooked to mush. The larger the piece, the longer the cooking time, though the crunchier the outside will be. As with all roasted vegetables, give them plenty of space on the baking sheet so that the moisture doesn’t steam the neighboring pieces as it evaporates away while cooking. If your oven has a convection function, it will help wick the moisture away and make the outside crispier.