Preheat oven to: Slow Cooker
Combine flour, garlic powder, salt, and pepper. Toss beef in flour mixture.
Heat olive oil in a large Dutch oven or pot over medium-high heat. Shake off any excess flour from the beef and brown in small batches. Remove and set aside in a bowl.
Add the onions to the pot, adding more oil as needed, and cook until they begin to soften, about 3 minutes.
Add beef broth and red wine while scraping up any brown bits in the pan.
Stir in browned beef, potatoes, carrots, celery, tomato paste, and rosemary. Reduce heat to medium-low, cover, and simmer 1 hour or until beef is tender (up to 90 minutes).
Mix equal parts cornstarch and water to create a slurry. Slowly add the slurry to the boiling stew to reach desired consistency (you may not need all of the slurry, if you'd like a thicker stew, you can add extra).
Stir in peas and simmer 5-10 minutes before serving . Season with salt & pepper to taste.