In a large skillet, heat the olive oil over medium-high heat. Add the beef cubes and brown them on all sides, about 5-7 minutes. Transfer the browned beef to the slow cooker.
In the same skillet, add the chopped onion and garlic, sautéing for 2-3 minutes until softened. Add to the slow cooker.
Add the sliced carrots, diced potatoes, beef broth, tomato paste, Worcestershire sauce, thyme, rosemary, bay leaf, salt, and pepper to the slow cooker. Stir to combine.
Cover and cook on low for 8 hours or on high for 4 hours, until the beef is tender.
If you prefer a thicker stew, mix the cornstarch and water in a small bowl to create a slurry. Stir it into the stew during the last 30 minutes of cooking. Add the frozen peas if using, and cook until heated through.
Remove the bay leaf before serving. Taste and adjust seasoning if necessary.