Make a great side dish today with Zucchini & Onion Gratin!
A few weeks ago I spotted this delicious gratin on a cooking site and knew I had to try it. I had plenty of zucchini and onions that needed using, and since we were planning to grill steaks that night, the gratin seemed like the perfect side. The finished dish was incredible—the oven aroma alone had everyone excited, and the crispy cheese top kept people going back for seconds.
I simplified the original recipe slightly to reduce the number of steps while keeping the flavor intact. I cook with a toddler underfoot, so fewer steps and minimal fuss make a big difference. This version is straightforward, flavorful, and reliable when you want an easy vegetable side that feels special.
The combination of sweet onion, tender zucchini, lemon zest, thyme, and a crispy layer of shaved Parmesan is what makes this gratin stand out. It’s a simple recipe with fresh ingredients and an impressive result. Make it for your next meal and watch it disappear.
What do you need for Zucchini & Onion Gratin?
- Olive oil
- Large sweet onion, thinly sliced
- Tomato paste
- Grated lemon rind
- Fresh thyme
- Salt
- Freshly ground black pepper
- Zucchini, thinly sliced
- Shaved Parmesan cheese
Just a handful of fresh ingredients that combine into a flavorful, satisfying side.
Zucchini & Onion Gratin
Servings
6
Ingredients
- 1 Tbsp Olive Oil
- 1 Large Sweet Onion Thinly sliced
- 1 Tbsp Tomato Paste
- 2 Tsp Lemon Rind Grated
- 1 Tsp Fresh Thyme
- 1/4 Tsp Salt
- 1/4 Tsp Freshly Ground Black Pepper
- 1 1/2 Lbs Zucchini Thinly sliced
- 1/4 Cup Shaved Parmesan Cheese
Instructions
- Preheat the oven to 375°F (190°C).
- Heat the olive oil in a large cast iron skillet over medium heat. Add the sliced onion, tomato paste, grated lemon rind, thyme, salt, and pepper. Cook for about 5 minutes, stirring occasionally, until the onion begins to soften and the tomato paste is incorporated.
- Add the sliced zucchini to the skillet and cook another 5 minutes, until the zucchini is tender and everything is well coated with the oil and seasonings.
- Lightly spray a baking dish with nonstick spray or coat with a little oil. Transfer the zucchini and onion mixture into the dish, spread it evenly, and top with the shaved Parmesan cheese. Cover the dish with foil and bake for 25 minutes.
- Carefully remove the foil. Turn the oven broiler to high and return the uncovered dish to the oven for 1–2 minutes, watching closely, until the cheese is lightly browned and crisp on top.
- Remove from the oven and let rest a few minutes before serving. Enjoy warm as a side with grilled meats or as part of a vegetable-forward meal.
Nutrition
Did you make this recipe?
Tag your photos with #mommyhatescoooking on Instagram and follow @momhatescooking for more recipes and updates.