Season the pork with salt and pepper, to taste, the fennel seed, and the red pepper flakes. Dredge the pork in the flour.
Heat a large skillet with 3 tablespoons of the extra-virgin olive oil, over medium-low heat. When the oil ripples, add the pork and brown it for 5 to 6 minutes, turning once. Remove the pork to a plate. Add the remaining tablespoon of extra-virgin olive oil, then add the sliced fennel, onions, garlic, and thyme. Season with salt and pepper, to taste, and cook until softened, 8 to 10 minutes. Add the tomato paste and cook for 1 to 2 minutes more, then stir in the wine and scrape up the drippings. Stir in the citrus zest, juice, stock, and parsley. Reduce the heat, and simmer for 5 minutes, then add the pork and simmer for 3 to 4 minutes more. Turn off the heat and sprinkle with the chopped fennel fronds. Serve the pork and sauce in shallow bowls with crusty ciabatta for mopping.
Recipe courtesy of Rachael Ray