Vegan Shepherds Pie

Name: Vegan Shepherd's Pie
Ingredients: 1 tablespoon extra-virgin olive oil; 2 cups chopped fresh button mushrooms; 2 cups chopped yellow onions; 1 cup chopped carrots; 1 tablespoon minced garlic; 1 (15 ounce) can no-salt-added crushed tomatoes; 4 cups low-sodium vegetable broth; 1 ½ cups dried brown or green lentils, rinsed; 1 tablespoon chopped fresh thyme; 2 teaspoons chopped fresh rosemary; 1 teaspoon salt, divided; 1 teaspoon ground pepper, divided; 2 pounds Yukon Gold potatoes, peeled and quartered; 6 tablespoons vegan butter (such as Earth Balance); 2 tablespoons chopped fresh chives