Sounds nice, I've never used cauliflower rice before but cauliflower has a nice flavour that doesn't need salt, unlike rice which is pretty bland without seasoning or a good sauce.
Recipe time!
Cut up and boil a broccoli and cauliflower
Make a litre of white sauce and:
Add a teaspoon of English Mustard
Add a ridiculous amount of grated cheese
Add a teaspoon of pepper
Add more cheese
Mix it so the cheese is mostly melted into the sauce (it doesn't have to be smooth)
Throw the broccoli, cauliflower and the sauce into a casserole dish and give it a good mixing
Mix some breadcrumbs and grated cheese, sprinkle it on top (the breadcrumbs will give it a bit of crispiness)
Bake in the oven for about 20 minutes at 180C or 350F, or until the cheese topping is cooked to your satisfaction.