Heat grill to medium high.
Lightly brush or spray the peppers and red onions with olive oil.
Using tongs, set the onion quarters and red peppers slices cross-wise on the grill bars (so they don’t fall in. Another option is to use a grill pan, in which case you can chop the onion and red pepper as small as you like.)
Grill, flipping once, until well-browned or charred, per your preference.
Remove from heat and allow to cool.
Place all ingredients into a large attractive bowl and toss with dressing, below.
Sprinkle with pistachios.