In a large saucepot, render the pancetta. Add the beans and 5 cups of water. Simmer for 45 minutes. Strain the beans, reserve the liquid and discard the pancetta. Set aside.
In the same pot, heat the olive oil. Saute all the vegetables until the onions are transparent.
In a small bowl, dilute the tomato paste in the remaining 1/2 cup of water. Add to the vegetables. Add the spinach, the reserved bean liquid and chicken stock. Bring to a boil, then lower to a simmer. Add the beans, season with salt and pepper. Reduce by 1/4. Reserve.
Prepare the Cherry Tomato Vinaigrette. In a bowl, combine all the ingredients and toss gently. Reserve.
Preheat the oven to 400 degrees F. Brush the fish fillets with 1 tablespoon of olive oil. Season with salt and pepper. Place a medium saute pan over high heat. Add the remaining 1 tablespoon of olive oil and saute the fish, skin side down for 2 minutes. Transfer to the oven and bake until done, about 5 to 6 minutes. Do not turn the fish to ensure a crispy skin.
Prepare the escarole. In a large saute pan, over medium heat, add the olive oil. Saute the escarole until wilted. Season with salt.
Meanwhile, lay out 4 large soup plates and ladle 6 ounces of the white bean ragout on each plate. Lay 2 spears of escarole cross-wise. With a metal spatula, carefully place a fillet, skin side up, on top of the escarole. Spoon tomato vinaigrette across the fillet. Serve immediately.