1. Turn on broiler to low.
2. Coarsley chop cilantro.
3. Finely chop garlic.
4. Combine garlic, cilantro, salt, pepper in a small bowl. Mix together with fingers.
5. De-stem portabello mushrooms. Rub tops with damp paper towel to remove dirt.
6. Place mushrooms (stem-side up) on to broiler pan. Drizzle olive oil and 1/2 of the balsamic vinegar onto portobells.
7. Place under broiler 5-7 minutes.
8. Remove. Sprinkle cilantro mix onto portobellos. Drizzle with balsamic vinegar.
9. Place under broiler again for 6-7 minutes.
10. Serve with pinch of fresh cilantro.