A tender cut of beef like sirloin or rib-eye won't get tough as it simmers away in the stew. Serve with rice noodles, if you like.
Toss beef with cumin, coriander, 1/2 teaspoon salt and 1/4 teaspoon pepper in a medium bowl. Heat 1 tablespoon oil in a large pot over medium-high heat. Add the beef and cook, stirring occasionally, until browned on all sides, about 3 minutes. Transfer to a plate.
Add the remaining 1 tablespoon oil, onion and mushrooms to the pot. Cook, stirring occasionally, until the vegetables start to soften, 2 to 3 minutes. Add sweet potato, garlic and curry powder; cook, stirring, for 30 seconds. Add broth and scrape up any browned bits. Stir in the beef and any accumulated juices, coconut milk and the remaining 3/4 teaspoon salt and 1/4 teaspoon pepper. Bring to a boil. Reduce heat to maintain a simmer, partially cover and cook until the sweet potatoes are almost tender, about 7 minutes.
Stir in kale and cook until the beef and vegetables are tender, 5 to 8 minutes more. Serve with cilantro and lime wedges, if desired.