Pat the pork cubes dry with paper towels. Add the flour, salt, and black pepper to a large bowl or zip-top bag, then toss the pork until every piece is lightly coated.
Heat the olive oil in a cast iron skillet over medium-high heat until it shimmers. Working in batches, sear the pork in a single layer for about 2 minutes per side until deeply browned, then transfer to the slow cooker.
Lower the heat to medium and add the diced onion to the same skillet. Cook for 4 to 5 minutes until soft and translucent, then stir in the garlic and tomato paste and cook for 1 to 2 minutes until darkened and toasty.
Pour in about 1 cup of the beef broth to deglaze, scraping the bottom of the pan with a wooden spoon to lift every browned bit. Pour this mixture into the slow cooker over the pork.
Add the remaining beef broth, Worcestershire sauce, smoked paprika, dried thyme, and bay leaves to the slow cooker. Add the potato chunks, carrot coins, and sliced celery, then stir gently so everything is evenly distributed and mostly submerged.
Cover the slow cooker with the lid and cook on LOW for 8 hours, or on HIGH for 4 hours, until the pork is fork-tender and the vegetables are soft. Resist the urge to lift the lid during cooking.
In a small bowl, whisk the cornstarch with 2 tablespoons of cold water until smooth with no lumps. Remove and discard the bay leaves.
Stir the cornstarch slurry into the stew, then scatter in the frozen peas. Cover and cook on HIGH for a final 15 to 20 minutes, until the broth thickens to a gravy consistency and the peas are heated through.
Taste and adjust with more salt and pepper if needed, then garnish each bowl with chopped parsley.