Preheat your oven to 350°F (175°C).
Grease a baking dish lightly with butter.
In a pot, bring water to a boil and cook the sliced squash and chopped onions for about 5-7 minutes, until tender.
Drain and set aside.
Melt butter in a pan over medium heat.
Stir in the boiled squash and onions.
Add garlic powder, salt, and pepper, mixing well.
Mix in the shredded cheddar cheese and sour cream.
Stir until the cheese melts and everything is well combined.
Transfer this mixture to the greased baking dish.
Top with crushed Ritz crackers, spreading them evenly across the surface.
Bake in the oven for 25-30 minutes, or until the top is golden brown.
Serve hot.