In a small bowl stir together the minced garlic and olive oil. Clean portobello mushrooms by brushing them with a paper towel. Remove the stem and discard. Brush the mushroom caps with the garlic and olive oil mixture. Place them on a baking sheet with gills facing upward Sprinkle 1/4 cup of diced tomatoes on each mushroom cap.
Bake for 13 minutes in the preheated oven. Remove from the oven and spread blue cheese on top of the tomatoes. Return the mushrooms to the oven and bake until the cheese is melted and bubbly. Allow the mushrooms to cool for a few minutes before serving.
