Cut 5 slits in the roast and stuff with the garlic cloves. Sprinkle with salt and pepper.
Heat a Dutch oven over medium-high heat and add the oil. Sear the roast on all sides until a rich brown color. Add the hot water, bay leaves and bell pepper and bring to a boil. Cover, reduce the heat and simmer until the roast is very tender, about 3 hours. During cooking, you want to make sure you keep the level of liquid that you started with. You may have to add up to another 1 1/2 cups water. Do not let the liquid cook out.
Transfer the roast to a cutting board to rest. Discard the bay leaves and bell pepper from the pot. Sprinkle in the flour and cook, whisking, until thickened. You may need to add more flour until you reach the desired thickness of gravy. Be careful not to add too much, since it will thicken faster than you may expect. Season with salt and pepper.
Slice the bread down the center and warm slightly in the oven. Thinly slice the roast. Spoon the gravy over the cut sides of the bread and spread with some mayonnaise. Load the bottom half with sliced beef and top with lettuce, tomatoes and pickles. Cover with the top half of the bread. Cut into 6 pieces and wrap with butcher paper or parchment paper.