In a large skillet, brown the beef until no longer pink. Drain off excess grease. Add onion, garlic, and zucchini and saute for 3-5 minutes.
Add carrots and peas and stir together.
Add Worcestershire sauce and tomato paste. Season with thyme and cook for about 1 minute.
Add broth and simmer until 10-15 minutes or until sauce has thickened. Taste and adjust seasoning.
Transfer beef mixture to a deep casserole dish. You can use an 8×8 square pan, a casserole or you can make individual servings.
Spoon mashed potato on top of beef. Sprinkle with grated Parmesan cheese and cheddar cheese. Place the dish on a cookie sheet in case it bubbles over while baking.
Bake in a 375° F oven for 20 minutes or until top is brown and heated through. The sides may be bubbly. Garnish with chopped scallions.
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Notes
Instead of grated zucchini, you can use grated carrot. Dried rosemary would be a delicious addition as well.
Wine can be used instead of or in addition to the broth.