Fill a large pot with water and bring to a rolling boil.
Add sliced yellow squash and zucchini, and bring back to a boil
Cook vegetables until tender, about 15-20 minutes. Drain and transfer vegetables to a large bowl.
Mix Cheddar cheese, butter, eggs, sugar, and salt with the cooked vegetables using a large spoon; stir until butter has melted. Gently fold the crushed RITZ crackers into the mixture until the liquid has been absorbed. Pour mixture into a 2-quart casserole dish; Sprinkle bread crumbs on top.
Bake in the preheated oven until topping is lightly browned and cheese is melted, 30 minutes.