Preheat oven to 400 F. Line baking sheets with foil & spray with cooking oil.
Place the cauliflower slices onto a large baking sheet. They need lots of space between them & shouldn’t overlap so use 2 large baking sheets if needed.
Spray cauliflower steaks lightly with the avocado or olive oil & season with sea salt, pepper & Italian seasonings.
Roast for 20-25 minutes in preheated oven, until golden brown on the sides.
In a mixing bowl add mushrooms, minced garlic, a pinch of sea salt and pepper, then toss to coat well.
Sprinkle roasted cauliflower steaks with cheese & top the cheese with roasted mushrooms & garlic mixture.
Return to the oven for 2-3 minutes until cheese is melted & bubbly.
Sprinkle with sliced green onion. Since I had some roasted chicken on hand, I sliced it & placed a small amount on top of each mushroom steak just before returning to oven for the last 2-3 minutes. The chicken was already warm so it worked out well.