This Tomato, Potato, Zucchini, Summer Squash Casserole is the kind of comforting, colorful bake that makes simple vegetables feel special. Sliced zucchini and summer squash bring a tender, garden-fresh bite, while potatoes add hearty structure that helps the casserole feel satisfying enough for a full meal. Tomatoes soften as they bake, releasing juices that mingle with herbs and aromatics, creating a naturally flavorful base without needing anything complicated. The onion and garlic are quickly sautéed first to deepen their sweetness and aroma, then everything is layered and finished with a generous blanket of mozzarella and Parmesan that turns bubbly and golden in the oven. It’s a straightforward dish with a beautiful payoff: soft vegetables, savory seasoning in every bite, and a cheesy top that’s hard to resist.
Ingredients
- 2 medium zucchinis, sliced
- 2 medium summer squashes, sliced
- 2 large tomatoes, sliced
- 2 medium potatoes, thinly sliced
- 1 medium onion, chopped
- 3 cloves garlic, minced
- 1 teaspoon dried oregano
- 1 teaspoon dried basil
- 1 teaspoon salt
- ½ teaspoon black pepper
- 1 cup shredded mozzarella cheese
- ½ cup grated Parmesan cheese
- 2 tablespoons olive oil
- Fresh basil leaves for garnish (optional)
Prep Time
15 minutes
Cook Time
50 minutes
Total Time
1 hour 5 minutes
Servings
6 servings
Kcal
180 calories (per serving)
Instructions
- Preheat the oven.
Set your oven to 375°F (190°C). Preheating is important here because the casserole needs steady heat right away to start softening the potatoes while the vegetables release their juices evenly. - Sauté the onion and garlic (the flavor foundation).
Place a large skillet over medium heat and add the 2 tablespoons olive oil. Once the oil is warm, add the chopped onion and minced garlic. Sauté for 3–4 minutes, stirring frequently, until the onion looks translucent and smells sweet and savory. Watch closely so the garlic becomes fragrant without browning. - Season and combine the sliced vegetables.
In a large mixing bowl, add the sliced zucchini, summer squash, tomatoes, and thinly sliced potatoes. Spoon in the warm sautéed onion and garlic mixture. Sprinkle over the dried oregano, dried basil, salt, and black pepper. Toss thoroughly so the seasonings and aromatics are distributed across all the slices. Take a moment to separate slices that stick together—especially potatoes—so they bake evenly.
- Prepare the baking dish.
Use a 9×13-inch baking dish and grease it well. This helps prevent sticking and makes serving cleaner, especially once the cheese melts into the edges. - Layer the first half and add cheese.
Spread half of the vegetable mixture evenly across the bottom of the greased dish. Aim for a fairly level layer so the casserole cooks uniformly. Sprinkle half of the shredded mozzarella over the vegetables, letting it fall into gaps so the cheese helps “hold” the layer together as it bakes. - Finish layering and top the casserole.
Add the remaining vegetable mixture on top, distributing it so you have a balanced mix of zucchini, squash, tomato, and potato across the surface. Finish with the remaining mozzarella, then sprinkle the grated Parmesan evenly over the top. The Parmesan helps create a lightly crisp, golden finish as it bakes uncovered. - Bake covered, then uncovered.
Cover the dish tightly with aluminum foil and bake for 30 minutes. This covered stage traps steam, helping the potatoes soften and the vegetables become tender without drying out. After 30 minutes, carefully remove the foil (watch for hot steam). Return the dish to the oven and bake for another 15–20 minutes, until the vegetables are tender and the cheese is bubbly and golden. - Rest, garnish, and serve.
Remove the casserole from the oven and let it cool for about 5 minutes. This short rest helps the layers settle so servings hold together better. If you’d like, garnish with fresh basil leaves just before serving for a fresh, aromatic finish.
Notes
- You can substitute the mozzarella cheese with cheddar or a dairy-free cheese alternative for a different flavor profile.