Preheat grill to medium-high heat.
Clean portobello mushrooms and remove stems.
Brush mushrooms with olive oil and season with salt and pepper.
Grill mushrooms for 5-7 minutes on each side until tender.
Rinse quinoa under cold water.
In a pot, bring vegetable broth to a boil, add quinoa, reduce heat, cover, and simmer for 15 minutes.
Fluff quinoa with a fork and let it cool.
In a bowl, combine quinoa, red bell pepper, red onion, and parsley.
Drizzle with balsamic vinegar and mix well.
Serve grilled mushrooms topped with quinoa salad.