Step 1

Season short ribs with salt and pepper on both sides.

Step 2

Heat olive oil and sesame oil in a pot over medium-high heat and cook short ribs in batches until browned on all sides, 5 to 8 minutes. Place short ribs in a slow cooker.

Step 3

Stir together soy sauce, vegetable broth, rice vinegar, brown sugar, garlic, ginger, and crushed red pepper flakes in a bowl. Pour sauce over short ribs. Cover slow cooker.

Step 4

Cook on High until ribs are cooked through, about 4 hours. Remove ribs from sauce and keep warm.

Step 5

Pour sauce into a pot and cook on medium-low heat until reduced, about 5 minutes. Remove as much grease as possible. Mix cornstarch and water together in a small bowl until smooth. Pour into sauce and cook until thickened, 1 to 3 minutes.

Step 6

Pour sauce over short ribs and sprinkle sliced green onions on top.