In a large skillet, heat the vegetable oil over medium-high heat. Add the beef cubes and brown them on all sides for about 5-7 minutes until they achieve a nice golden color.

In the same skillet, add the chopped onion, garlic, and ginger. Sauté until the onion becomes translucent, approximately 3-4 minutes.

In your slow cooker, combine the browned beef with the sautéed onion mixture. Add the curry powder, cumin, coriander, turmeric, cayenne pepper, diced tomatoes, coconut milk, tomato paste, brown sugar, salt, and pepper.

Stir everything together until well combined, ensuring the beef is well coated.

Cover and cook on low for 6-8 hours or on high for 3-4 hours.

Before serving, taste the curry and adjust the seasoning as necessary.

Serve the curry hot, garnished with fresh cilantro.