Preheat the oven to 350°F. 

Score the pork belly skin diagonally in a diamond pattern at 1/2-inch intervals. Season generously with salt and pepper, rubbing it well into the skin.

In a hot roasting pan over medium-high heat, combine the fennel, bay leaves, garlic, star anise and half the fennel seeds with a little olive oil and heat until aromatic, about 2 minutes. Push the fennel mixture to the side of the pan.

Add the pork, skin side down, to the pan and cook until the meat is turning golden brown, 5 to 7 minutes. Turn the pork over and season the skin again with salt. Add the wine, stirring to scrape up any browned bits (be careful not to get the pork skin wet). Bring to a boil, then pour in enough stock to come up to the layer of fat just below the skin and bring to a boil again.

Transfer the pan to the oven and cook for 2 1/2 hours. Transfer the meat to a warm plate and let rest.

Spoon off any excess fat in the roasting pan, or drag a slice of bread along the surface of the cooking juices to absorb it. Heat the sauce in the roasting pan and whisk in the mustard. Adjust the seasoning with salt and pepper. Remove and discard the star anise. Pour the sauce into a serving pitcher. 

Arrange the pork on a bed of arugula and garnish with the mango-pineapple salsa. Serve the red wine sauce on the side. 

In a bowl, combine the onion, mango, pineapple and cilantro, and season to taste with salt and pepper.