Combine sherry vinegar, 3 tablespoons olive oil, and minced garlic in a jar with a lid and shake until blended. Set aside.

Place lentils, chicken broth, water, and 1 tablespoon olive oil in a saucepan and bring to a boil. Reduce the heat to low and simmer, covered, until the lentils are just tender to the bite, about 20 minutes. Do not overcook. Remove from heat, drain, and cool for at least 30 minutes. Transfer cooled lentils to a mixing bowl.

Stir in the dressing, chives, and cilantro; mix well. If you're serving the salad immediately, add the goat cheese and tomatoes. If you're preparing the recipe ahead of time, refrigerate the salad and add the goat cheese and tomatoes just before serving.