Pat the beef cubes dry with paper towels. Season generously with salt and black pepper.

Heat 1 tablespoon of olive oil in a large skillet over medium-high heat. Brown the beef in batches until seared on all sides, about 2-3 minutes per batch. Do not overcrowd the pan. Remove beef and place into the slow cooker insert.

Add the remaining 1 tablespoon of olive oil to the same skillet (add a little more if needed). Reduce heat to medium. Add the chopped onion and cook until softened and translucent, about 5-7 minutes.

Stir in the minced garlic and grated ginger. Cook for another 1-2 minutes until fragrant, being careful not to burn the garlic.

Add the curry powder, garam masala, ground cumin, ground coriander, turmeric powder, and cayenne pepper (if using) to the skillet with the onions, garlic, and ginger. Cook for 1 minute, stirring constantly, until the spices are very fragrant. This step helps to deepen the flavor of the spices.

Transfer the aromatic and spice mixture from the skillet to the slow cooker with the browned beef.

Add the diced tomatoes (undrained), full-fat coconut milk, beef broth, and tomato paste to the slow cooker. Stir everything gently to combine.

Cover the slow cooker and cook on LOW for 6-8 hours, or on HIGH for 3-4 hours, until the beef is fork-tender. The longer it cooks on low, the more tender the beef will be.

Once cooked, stir in the fresh lime juice. Taste and adjust seasoning with additional salt or pepper if needed.

Garnish with fresh chopped cilantro before serving.

Serve hot over basmati rice, with naan bread, or alongside steamed vegetables.