
Preheat oven to 400˚F.
Lightly grease a 9x13 baking dish; set aside.
Add water to a large pot, filling it about halfway up, and bring to a boil.
Add broccoli florets and cauliflower florets to the boiling water.
Bring to a boil and continue to cook for 3 minutes. Drain well and set aside.
In the meantime, add vegetable oil to a skillet and heat over medium-high heat.
Stir in onions and cook for 2 minutes.
Add garlic and cook for 20 seconds.
Stir in smoked sausage and cook for 3 minutes, or until browned on all sides. Stir frequently.
Transfer broccoli, cauliflower, plus sausage mixture to previously prepared baking dish.
In a mixing bowl combine cream cheese, mayonnaise, 1 cup shredded cheese, dijon mustard, salt, and pepper; mix until thoroughly incorporated.
Stir the cream cheese mixture into the broccoli mixture; stir around until everything is well combined. Add remaining shredded cheese on top.
Bake for 12 to 15 minutes, or until cheese is melted and top is golden brown.
Remove from oven and serve.