For the beef: Combine the chuck, bell peppers, onions, garlic, tomatoes, Italian seasoning, fennel seeds, 2 1/2 teaspoons salt, and some pepper in a slow cooker. Cook on the low setting for 8 hours. Use a ladle to remove some of the excess fat from the surface, then coarsely shred the beef with two forks. Season with salt and pepper.
For the aioli: Place the egg, garlic and Dijon in a food processor and pulse to combine. With the motor running, add the olive oil and vegetable oil in a very slow steady stream until it is all incorporated. Add the in the giardiniera to the food processor and pulse until chopped. Season with salt and pepper.
Spread about 2 tablespoons of the aioli on both sides of the bread and then make sandwiches with the shredded beef. Serve immediately.
In a small bowl, mix together the basil, marjoram, oregano, parsley, granulated garlic, rosemary, thyme and red pepper flakes. Store in a jar with a tight-fitting lid.