Thinly slice the summer squash and place it in a mixing bowl. Squeeze out excess moisture with your hands or a clean towel to prevent sogginess.
In a small skillet, toast the breadcrumbs over medium heat until golden and crispy, stirring frequently to prevent burning. Set aside.
In a mixing bowl, whisk together the eggs and melted butter until well combined and slightly frothy. This will help bind the casserole together.
Add the chopped onion, shredded cheese, herbs, and the squeezed squash to the egg mixture. Mix until evenly incorporated.
Pour the mixture into a hot skillet and spread it out evenly. Let it cook undisturbed for about 3-4 minutes, until the edges start to set and turn golden.
Sprinkle the toasted breadcrumbs evenly over the top of the squash mixture. Continue cooking for another 10-12 minutes until bubbling and golden brown on top.
Watch for crispy, browned edges and a bubbling top—these are signs it’s ready to serve. Carefully slide a spatula underneath to check the bottom for a golden crust.
Once cooked through and crispy on top, remove from heat and let it rest for a couple of minutes. Slice into squares and serve warm, enjoying the contrast of crispy crust and tender squash.
