Heat olive oil in a pan at medium low heat and add sliced onions. Stir the onions until they are coated with oil. Sprinkle a pinch of salt on the onions.
Stir the onions every few minutes or so. Cooking will take about 20 minutes. Add balsamic vinegar to deglaze the pan. Add sliced mushroom, and cook a few minutes more. Set aside to cool.
Make pizza crust per instructions. If using the Vegan Gluten Free Pizza Crust, bake for 10 minutes at 450° before adding toppings (if using store-bought, then follow those instructions).
Mix chipotle in adobo sauce with pumpkin puree. Add salt and pepper, to taste. Spread half on top of pizza crust and save the other half for another day, or to top 2nd pizza crust.
Top with half each of caramelized onions and mushrooms and save the rest, or top on 2nd pizza crust. Bake at 450° for 5 minutes more, or until heated through and crust is crispy.