Preheat the oven to 425 degrees F and line a small baking pan with lightly greased aluminum foil.
Prep mushrooms by removing the stems and gently scraping out the dark/brown part to make room for stuffing. Line them on the baking sheet and cook for 8 to 10 minutes.
In a medium saucepan over medium heat, heat the oil and add diced onions and tomatoes. Let cook for 3 minutes and add in tomato sauce/marinara.
Prep the kale by washing and chopping it into bite-sized pieces. Add it into the saucepan and let everything cook together for about 5 minutes.
Take the mushrooms out of the oven, you’ll notice they’re filled with “water” that’s totally normal. Just take a paper towel and dab each of them to remove the liquid. That’s why you bake them before stuffing, so they don’t get all soggy and gross.
Spoon the filling into each mushroom, you should have plenty to fill 6 medium-sized mushrooms. Optionally, top each with a little vegan cheese or any other pizza topping you enjoy.
Bake on broil for about 2 to 3 minutes, or until vegan cheese is bubbling/light brown. Let rest for a couple of minutes to cool.
Enjoy these plant-based pizzas as an appetizer, side, or snack for a delicious, crowd-pleasing, gluten-free, grain-free, vegan pizza!