Sprinkle beef with salt and pepper and dredge in flour.
Heat oil and brown beef. You may want to divide it into two batches so it browns evenly. Transfer to slow cooker.
Cool pan a little, then add onion, mushrooms and peppers and more oil if needed. Cook until onion is golden brown.
Add a bit more flour and mix with the vegetables. Add broth or water and stir until smooth. Season with salt and pepper.
Transfer vegetable mixture to slow cooker.
Deglaze pan with red wine.
Add tomato paste to slow cooker and stir. Cook for 7-8 hours on low.
Adjust seasoning as neccessary while it's cooking.
If goulash is too watery, make a slurry (mix flour or cornstarch with water or broth) , add to slow cooker and cook on high for 15-20 minutes.