Toss the cauliflower and red onions with olive oil, salt and pepper on a sheet pan.
Roast the cauliflower and red onions until they are lightly browned.
Roughly chop the cauliflower.
Cook the lentils on the stove. Rinse them in cold water and put them in a bowl.
Add the cauliflower, red onions, olives, pistachios and parsley to the lentils.
Whisk together the lemon garlic vinaigrette.
Stir the vinaigrette into the salad.