In a large skillet over medium high heat add oil and bring to a shimmer. Season roast on all sides with salt, black pepper, garlic powder, and onion powder.
Place roast in hot skillet and sear for 4-5 minutes on one side until brown. Turn roast over and cook an additional 3-4 minutes until brown. Sear sides for 1 minute each side. Turn off burner.
In the bottom of a 6 quart oval crockpot place half of the sliced onions. Place roast on top of the onions. Cover roast with remaining onion slices. Pour 4 cups beef broth over onions and roast. Pour French onion soup over onions and roast. Pour Worcestershire sauce over onions & roast.
Sprinkle with 1/4 – 1/2 tsp each of salt, black pepper, garlic powder, onion powder, and thyme.
Cover crockpot with lid and cook on high for 4-5 hours or on low for 7-8 hours until fork tender and falls apart.
Place baguette slices on a sheet pan. Top baguette slices with a handful of shredded cheese. Broil in oven until cheese has melted and golden in color.
Shred roast in crockpot. Serve over mashed potatoes and top with the toasted cheesy baguette slices.