Cauliflower Rice Skillet with Zucchini and Kielbasa

medium heads cauliflower

olive oil

kielbasa sausage, sliced into bite-size pieces

butter (half stick)*

juice from half a lemon

salt

pepper

cayenne pepper

dijon mustard

medium zucchini, sliced lengthwise and chopped

and 1/2 cups frozen peas

or 1 cup cheddar cheese, shredded