Preheat the oven to 350°F (175°C).
In a large skillet, heat olive oil over medium heat.
Add chopped onions and sauté until translucent.
Stir in minced garlic and cook for an additional minute.
Add diced squash to the skillet and cook until slightly tender.
In a bowl, whisk together eggs and milk.
Combine the squash mixture with egg mixture, cheese, salt, and pepper.
Pour the mixture into a greased baking dish.
Top with breadcrumbs and a sprinkle of cheese.
Bake for 30-35 minutes or until golden brown and set.