Fill a small saucepan 3/4 full of water and bring to a boil. Add broccoli and carrots and cook until crisp/tender about 3-4 minutes. Drain water and set aside.
Combine onion, cream of mushroom soup, mayonnaise, and cheese.
Pour melted butter into the bottom of a medium sized or square baking dish and place broccoli and carrots on top of butter.
Spread mayonnaise and soup mixture over vegetables and top with crushed saltine crackers.
