Heirloom Grape Tomato Salad

Name: Heirloom Grape Tomato Salad
Ingredients: 1 lemon; 1/4 cup apple cider vinegar; 1 garlic clove, minced; 1/2 teaspoon Dijon mustard; 1 tablespoon chopped chives; 1/4 cup chopped fresh basil leaves; 1/2 cup plain yogurt; 1 cup extra-virgin olive oil; Freshly ground black pepper; 1 pint red grape or cherry tomatoes, halved (preferably an heirloom variety such as Tommy Toe); 1 pint yellow grape tomatoes, halved; 3 stalks celery, cleaned, leaves removed and thinly sliced; 6 scallions, white and tender green parts only, sliced