In large skillet over medium heat, heat the olive oil for about 2-3 minutes.Add half of beef cubes. Let cook without disturbing for about 3-4 minutes or until a brown crust begins to form. Turn once. Brown an additional 3-4 minutes and place in slow cooker.Repeat with remaining meat.To the already hot skillet, add your onion, carrots, mushrooms and garlic. Stirring to remove any flavorful brown bits from the bottom of the skillet.Add tomato paste and sauté until incorporated into the veggies - it will be a bit thick, just keep stirring!Toss all that on top of the beef in your slow cooker.Add broth and barley.Stir until well combined.Cook on low for about 6 hours or high for about 4. Time will vary depending on how hot your slow cooker gets. Check the meat, when tender - its done! Season to taste.