When I decided to grill the portobellos, I had considered making a raspberry vinaigrette but I decided to just use the berries right in the salad. So use any favourite neutral salad dressing or use this vinaigrette recipe.
I don't normally clean mushrooms too much but in this case they seemed awfully dirty. Just wipe them with a damp paper towel to clean.
I also removed the gills - this isn't absolutely necessary and I often don't bother. Definitely remove the gills if you are using them for a mushroom risotto - otherwise you'll end up with muddy looking rice!
Either toss with some olive oil so the mushrooms are lightly coated or just use some olive oil in the pan and pour a bit extra into the cavity (and sprinkle with salt). Grill until well browned and the texture has softened fully.
Allow the mushrooms to cool then slice. Toss with mixed greens, fresh raspberries, pieces of boursin cheese (I used pepper boursin) and your favourite vinaigrette. Add pepper if you like it!