Preheat oven to 325F. Heat 1 Tbsp oil over medium heat, then add pancetta and cook until crispy on all sides, about 5 minutes. Use a slotted spoon to transfer pancetta to a paper-towel lined plate or bowl.
Increase heat to medium-high, then add onion and shallot. Cook 2 minutes, until translucent, then add garlic. Cook 1 minute more.
Add anchovy paste, then use a wooden spoon to break up and dissolve. Next, add tomatoes, beans, cooked pancetta, thyme, and bay leaf, then toss gently to combine. Season with 1 tsp kosher salt and ¼ tsp freshly ground black pepper.
Nestle uncooked chorizo into sauce, then add ½ cup chicken stock.
Meanwhile, make breadcrumbs. Combine 3 cups fresh bread crumbs with 6 Tbsp melted unsalted butter, ½ tsp kosher salt, and lemon zest, then toss to evenly coat. Sprinkle half the breadcrumb mixture evenly on top of chorizo and sauce, then bake for 1 hour. Sprinkle on remaining breadcrumbs directly on top of cassoulet, then bake an additional hour. Sprinkle with parsley, then serve immediately.