Start by slicing the summer squash into thin rounds, then toss them into a mixing bowl.
Using your hands or a spoon, gently squeeze out excess moisture from the squash to help it crisp up during baking.
In a skillet, heat the oil over medium heat and sauté the minced onion until translucent and fragrant, about 3-4 minutes.
Add the sliced squash to the skillet and cook until they just start to soften and develop a light golden color, about 5 minutes. The squash should smell nutty and slightly caramelized.
Remove the skillet from heat and let the sautéed squash and onions cool slightly.
In a mixing bowl, combine the sautéed squash and onions with the heavy cream, grated cheddar cheese, chopped herbs, salt, and pepper. Mix until well combined and the ingredients are evenly distributed.
Transfer the mixture into a greased baking dish, spreading it into an even layer.
Sprinkle the bread crumbs evenly over the top of the casserole for crunch and a golden finish.
Place the casserole in a preheated oven at 375°F (190°C) and bake for about 25-30 minutes, or until the top is bubbling and golden brown.
Once baked, let the casserole rest for a few minutes to settle, then serve hot, enjoying the crispy top and tender squash inside.
