Layer onions and carrots on the bottom of the slow cooker.
Sprinkle roast with salt and pepper. Heat a large saucepan to high heat. Using tongs, sear all sides of the roast for 10 seconds each side.
Place roast on top of onions and carrots. Add cream of mushroom soup, french style green beans, dry onion soup mix, beef broth and the red potatoes last.
Set on Low for 8-10 hours or High for 3-4 hours
Gravy
Remove the roast and vegetables from slow cooker and set aside.
Pour 2 cups of roast juices into a saucepan. Set heat to high, until boiling.
In a bowl, add water and gradually whisk in flour until smooth.
Slowly add flour mixture to boiling juices in the saucepan and whisk continuously until desired thickness (1-2 minutes). Remove from heat and pour into a seperate bowl and serve.