Coat your halibut with olive oil spray. Rub the fleshy side of your halibut generously with your favorite fish rub. Let sit so the flavors soak in (just a few minutes while you prep the veggies).
Put the cauliflower, mayo, mustard salt and pepper in a bowl. Stir to coat the cauliflower. Then transfer the mixture to an ovenproof glass pan. Sprinkle on the cheese and the red pepper bites.
When you are ready to cook the fish, spray a cast iron pan with olive oil spray. Put the fish in fleshy side down (skin side up). Put the heat on Medium High and let the fish cook for 5 minutes. You are searing the flavors and the rub into the top of the fish.
After 5 minutes, turn fish over carefully with a spatula (skin side down).
Now put both pans (fish and veggies) in an oven set at 400 degrees and roast for 15 to 20 minutes. You'll know the fish is done when it's white all the way through and flakes off of the skin easily. The cauliflower should be slightly al dente, and the cheese will form a crust of sorts over the vegetables. The red gives it color or you'd have a dull, monochromatic meal and we can't have that!