Preheat your oven to 375°F (190°C).
Clean the Portobello mushrooms and remove the stems.
In a bowl, mash the avocados with a fork until smooth.
Add diced tomatoes, chopped red onion, cilantro, lime juice, minced garlic, salt, and pepper to the mashed avocados. Mix well to combine.
Brush the Portobello mushroom caps with olive oil on both sides and place them on a baking sheet.
Spoon the guacamole mixture into each mushroom cap, filling them generously.
Bake in the preheated oven for about 20-25 minutes, or until the mushrooms are tender.
Serve the Guacamole Portobello Mushrooms hot, garnished with extra cilantro, tomato or a squeeze of lime juice if desired.
Enjoy!
