Preheat oven to 400 degrees F
Line a baking tray with a sheet of parchment paper.
Cut the small stems from the mushroom caps and place the caps top side down on top of the parchment paper on the baking tray.
Layer 2 veggie burgers on top of each mushroom.
Add a slice of tomato and a slice of red pepper to each layer. Top with one of the small mushroom stems.
Cover with aluminum foil and bake in the oven for 1 hour.
Remove the foil from the mushroom burgers.
Turn the oven to the Low Broil setting.
Broil the mushroom burgers for 10 minutes and they are ready to serve.
Carefully transfer the mushroom burgers to plates (using a spatula may help).
Some rearranging of the vegetable stack may be necessary if it has spread out.