Heat a medium non-stick skillet over medium-high heat.
Add mushroom stems, onions, garlic and 1 tbsp of veggie stock. Cook 8 to 10 minutes, stirring occasionally, until sofetened, adding small amounts of veggie stock to prevent sticking.
Meanwhile, heat a small non-stick skillet over medium-low heat. Add pine nuts and toast, shaking often to prevent burning. Remove pine nuts when lightly browned from pan and set aside.
Stir in spinach, roasted red peppers, toasted pine nuts, balsamic vinegar and black pepper to taste. Heat for an additional 2 minutes.
Arrange mushroom caps on a non-stick baking pan or a baking dish. Divide filling evenly between mushrooms, rounding top with a spoon. Add half of a cherry tomato to each mushroom cap.
Bake for 20-25 minutes, or until softened and juicy.
Serve immediately. Enjoy!
Recipe by Pure Thyme at https://purethyme.com/2012/06/spinach-stuffed-mushrooms.html