Preheat oven to 400 degrees. Cut peppers in half lengthwise, scoop out and discard the seeds and thick membranes and arrange them, cut side up, on a foil-lined baking pan. Drain the mushrooms and drizzle a little of the marinade over peppers. Bake 20 minutes, or until peppers are just tender, but still hold their shape.
Meamwhile, put couscous in a bowl, bring the vegetable broth to a boil and pour it over. Cover the bowl and leave it for 5 minutes to soak. Stir in the mushrooms, diced if large, ricotta salata and parsley, taste and add salt and pepper as needed. Spoon mixture into pepper halves and return them to the oven for 5 to 10 minutes or until cheese melts. Serve warm or at room temperature as an appetizer course or as part of a buffet.