Whisk together the olive oil, vinegar, Italian seasoning, Dijon mustard, garlic, salt, sugar, and pepper in a small bowl.
In a large bowl, combine the cauliflower, cherry tomatoes, cherry pepper halves, zucchini, carrots, and onion.
Add the dressing to the vegetables and toss gently to coat.
Cover and refrigerate for 2-24 hours. Stir every hour.