In a large bowl, combine beef, yogurt, garam masala, cumin, coriander, turmeric, salt, and pepper. Mix well and let marinate for at least 1 hour or overnight in the refrigerator.

In a skillet, heat vegetable oil over medium heat. Add chopped onion and sauté until translucent, about 5 minutes. Stir in garlic and ginger, cooking for another 1-2 minutes until fragrant.

Transfer the sautéed onion mixture to the slow cooker. Add the marinated beef, diced tomatoes, beef broth, and coconut milk. Stir to combine.

Cover and cook on low for 8 hours or high for 4 hours until the beef is tender.

Stir in peas during the last 30 minutes of cooking. Garnish with fresh cilantro before serving. Serve with rice or naan.