For the preppy joes: In a large saucepan or Dutch oven over medium-high heat, heat the olive oil. Add the ground sirloin and cook until mostly browned, about 5 minutes. Add the pepperoncini, tomato paste, garlic, onion and bell pepper and cook, stirring, for another minute.
Meanwhile, in a medium bowl, whisk together the tomato puree, brown sugar, sherry vinegar, Worcestershire, paprika, cayenne, onion powder, garlic powder, coriander, clove and 1/2 teaspoon freshly ground black pepper. Pour the sauce mixture over the meat and stir until evenly coated. Season with salt and additional pepper. Bring to a simmer, cover and cook, stirring occasionally, until heated through and thickened, about 20 minutes.
For the spicy Brussels sprout slaw: In a small bowl, combine the sour cream, chipotle, mayonnaise and red wine vinegar and whisk until evenly incorporated. Season with salt and pepper.
In a medium bowl, combine the Brussels sprouts, scallions, cilantro and jalapeno. Season with salt and pepper, then dress with the chipotle pepper crema as desired.
For the bread: Preheat the oven to 350 degrees F.
Brush both sides of the bread with melted butter and sprinkle with garlic powder. Put on a baking sheet fitted with a wire rack and bake until lightly toasted and golden brown, 5 to 7 minutes.
Top the garlic toast with the meat mixture, followed by some of the Brussels sprout slaw. Garnish with parsley.