Place beef chuck roast into your crockpot. Add French Onion Soup, water, garlic powder, red pepper flakes and Kosher salt. Cook on medium-high for 8 hours, or until roast is cooked completely through.

Carefully remove roast from the crockpot and place in a large casserole dish. Remove 1 cup of au juice from the crock pot and add to the casserole dish. Taking 2 forks, begin shredding the chuck roast. Continue until chuck roast is in small, bite sized pieces.

Turn your oven on to "broil".

Butter each bread slice and place on a large cookie sheet. Place under the broiler for 2 minutes, or until bread starts to look toasted. Watch carefully as to not burn the bread.

Remove toasted bread from oven and top evenly with shredded roast beef, jalapeños, and mozzarella cheese. Return to the oven and broil until cheese is melted, approximately 1-2 minutes. Remove from oven and serve while warm. If desired, drizzle au juice over the sandwiches before serving.