Preheat and prep: Heat the oven to 425°F (220°C). Lightly grease a 9x13-inch casserole dish.

Roast the cauliflower: Toss florets with 1–2 tablespoons oil, a big pinch of salt, pepper, and a little smoked paprika. Spread on a sheet pan. Roast 18–22 minutes until tender with browned edges. Transfer to the casserole dish.

Sauté veggies: Heat 1 tablespoon oil (and butter if using) in a large skillet over medium-high. Add onion, peppers, and mushrooms with a pinch of salt. Cook 7–9 minutes, stirring, until softened and a bit caramelized. Stir in garlic for 30 seconds. Move veggies to a bowl.

Cook the beef: Season sliced beef with salt, pepper, and a pinch of onion powder. In the same hot skillet, sear the beef in batches 1–2 minutes per side until just browned. Don’t overcook—it will finish in the oven. Return all beef to the pan.

Make the creamy sauce: Add Worcestershire and beef broth to the skillet, scraping up browned bits. Reduce by about one-third, then lower heat. Stir in cream cheese until smooth and silky. Taste and adjust salt and pepper.

Combine: Add the sautéed veggies back to the skillet and toss with the beef and sauce. You want everything lightly coated, not soupy.

Assemble the casserole: Layer half the provolone over the roasted cauliflower. Spoon the beef-and-veg mixture evenly on top. Finish with remaining provolone and the shredded mozzarella or Jack.

Bake: Reduce oven to 375°F (190°C). Bake 12–15 minutes until the cheese is melted and bubbling around the edges.

Brown the top (optional): Broil 1–2 minutes for golden, bubbly cheese. Watch closely.

Rest and serve: Let it sit 5 minutes to set. Sprinkle with chopped parsley and a pinch of red pepper flakes if you like heat. Serve warm.