In a medium skillet, add the ground beef and cornstarch, and cook over medium-high heat. Sauté until the beef is fully browned, about 3-5 minutes.
Pour the cooked ground beef into the slow cooker. Add the vegetable oil, garlic, ginger, soy sauce, water, brown sugar, carrots and chili sauce or flakes (optional). Stir inside the slow cooker until everything is well-mixed.
Cover the slow cooker, and cook on high power for 3 hours. Avoid opening the lid until at least 2 ½ hours through. After then, you may remove the lid and stir. If the beef is too dry, add another ¼ cup water.
Allow to cook for the remainder of the time, until the sauce has thickened and starts to simmer along the edges.
Remove the lid, and serve in individual bowls with fresh- steamed white or brown rice. Garnish with chopped green onions and sesame seeds.
Pro-tip: Adding cornstarch to the beef at the beginning of cooking helps give the Mongolian sauce a thick consistency.
Pro-tip: Substitute sliced flank steak for ground beef for a more traditional Mongolian beef.
