Pat the beef cubes dry with paper towels and season them with kosher salt and black pepper.
Heat the vegetable oil in a large skillet over medium-high heat. Working in batches, brown the beef cubes on all sides, about 5 minutes per batch. Transfer browned beef to the slow cooker.
Add the chopped onion to the skillet and cook until softened, about 5 minutes. Add the minced garlic and cook for 1 minute more.
Sprinkle the flour over the onion and garlic mixture and stir to coat. Cook for 2 minutes to remove the raw flour taste.
Pour in the red wine, scraping up any browned bits from the bottom of the skillet. Simmer until the wine is reduced by half, about 3-4 minutes.
Transfer the wine and onion mixture to the slow cooker with the beef. Add the beef broth, tomato paste, dried thyme, and bay leaves. Stir to combine.
Cover and cook on low for 6 hours.
After 6 hours, add the carrots, potatoes, and celery to the slow cooker. Cover and cook on low for an additional 1 hour, or until the vegetables are tender.
Remove the bay leaves. Stir in the thawed peas and chopped fresh parsley. Cook uncovered for 5 minutes to heat the peas through.
Taste and adjust seasoning with additional salt and pepper if needed. Serve hot.