Bring 3-4 cups water to boil. Place oats in the boiling water. Reduce heat, let simmer 30 minutes or more. (Refer to exact cooking direction on oats package).
Sprinkle beef with 1/4 teaspoon pepper. Heat 2 teaspoons oil in a Dutch oven over medium heat. Add the beef and cook, stirring often, until browned on all sides, about 2 minutes. Transfer to a bowl.
Add the remaining 2 teaspoons oil, onion to the pot and cook, stirring, until beginning to soften, about 2 minutes. Add carrot and cook, stirring, for 2 minutes more. Add spinach. Add thyme and cook, stirring, until the vegetables are beginning to brown, 1 to 2 minutes.
Add oats, broth, water, salt and the remaining 1/4 teaspoon pepper; bring to a simmer. Reduce heat to maintain a simmer; about 15 minutes. Return the beef and any accumulated juice to the pot and heat through, 1 to 2 minutes. Remove from the heat; stir in vinegar to taste.
You can store these in the refrigerator for 2 weeks, or the freezer for a few months. If storing in the freezer, remove the bars for about 20 minutes prior to serving.