Combine all the cauliflower ingredients in a 1-gallon freezer bag. Gently shake the bag until marinade is well mixed and cauliflower is fully coated. Set aside to marinate for 20 minutes.
In a separate freezer bag, combine all mushroom ingredients, reserving ½ tablespoon parsley to garnish. Gently mix the ingredients, make sure to keep the onions slices together. Set aside to marinate for 20 minutes.
Turn your Blackstone griddle to medium high heat. Spread a tablespoon of butter on the hot griddle, add your cauliflower. Let cook 5 minutes. Flip and using a basting dome to steam for 3 minutes, then let cook uncovered for 4-5 more minutes or until cooked through. Use a toothpick to check for doneness to your liking. Set aside and top with cheese to melt.
Add another 2 tablespoons of butter in two spots on the griddle. Cook the onions and mushrooms separately in a little butter until done to your liking. I like mushrooms cooked no longer than 3 minutes and onions to have a nice char but still a little crunch, about 4 minutes on each side. Remove from griddle once cooked.
Throw the spinach on the griddle in the flavored oil and butter left on the grill to cook for 1-2 minutes.
Arrange your vegetables on top of the spinach and garnish with tomatoes, cheese, and chopped parsley.
