The roasted yellow peppers in the dressing gives this salad a sweet balance in flavour and vibrant yellow colour!
Preheat oven to 375 degrees F.
Roast whole pepper and cipollini onions in middle rack of oven until browned, about 20-25 minutes, turning often. Transfer to bowl and cover with plastic wrap. Let pepper sweat for 5 minutes (the sweating will help remove the skin). Peel skin. Remove seeds.
Chop cippolini onion and set aside.
Add roasted pepper to food processor. Puree until smooth. Add sugar, salt and pepper, Dijon, cider vinegar and olive oil. Puree to combine.
Combine spinach, cipollini and tomatoes in large bowl. Toss salad with ½ the dressing and serve. Reserve remaining dressing to drizzle on top.