Shepherd's Pie

Name: Shepherd's Pie
Prep time: 20 min
Cook time: 20 min
Total time: 40 min
Cuisine: American
Ingredients: 1 1/2 pounds ground beef (or lamb); 1/2 cup onion (diced ); 1 cup zucchini (grated); 3 cloves garlic (finely minced); 1 1/2 tablespoons Worcestershire sauce; 2 tablespoons tomato paste; 1 teaspoon fresh thyme (or 1/2 tsp dried); 2 cups beef broth; 2 teaspoons salt (or to taste); 5 ounces carrots (frozen, 1 cup, not thawed); 5 ounces peas (frozen, 1 cup, not thawed); 3 cups mashed potatoes; 1/4 cup cheddar cheese (finely grated); 2 tablespoons grated Parmesan cheese