Pre-heat oven to 425 degrees F.
Unroll dough with oven-safe parchment paper onto an ungreased large cookie sheet (the dough bakes on the paper).
Brush with olive oil and bake 7 minutes.
Remove from oven.
Melt butter in a large non-stick skillet over medium-high heat.
Once melted, add onions and salt.
Cook 5 minutes, stirring occasionally, until onion has started to soften.
Add mushrooms and cook 7 minutes or until mushrooms and onions are golden brown and soft.
Stir in garlic and remove from heat.
Taste and re-season, if necessary.
Spread mushroom mixture evenly over dough.
Evenly sprinkle with spinach, mozzarella cheese and parmesan cheese.
Bake for an additional 7 to 12 minutes or until cheese is melted and crust is golden brown.
Garnish with thyme and red pepper flakes.
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