Heat oven to 425 degrees.
On a rimmed baking sheet, drizzle red pepper slices and cauliflower florets with 2 tablespoons oil and season with salt and pepper. Roast until golden and tender, 18 to 20 minutes.
In a bowl, whisk together remaining 2 tablespoons oil and lemon juice. Season with salt and pepper. Arrange roasted red peppers and cauliflower on a platter.
Top with olives, almonds, and parsley. Drizzle with dressing.