1. Heat a large Dutch oven over high heat. Add 1 tablespoon oil; swirl to coat. Sprinkle beef with 1/2 teaspoon salt and pepper. Add half of beef to pan; cook 4 minutes, browning on all sides. Remove from pan. Repeat procedure with remaining 1 tablespoon oil and beef.
2. Reduce heat to medium. Add onion and garlic; cook 3 minutes or until soft, scraping pan to loosen browned bits. Add 2 teaspoons mustard seeds, coriander, and cumin; cook 1 minute. Stir in remaining 1 teaspoon salt, beef, sweet potato, stock, and tomatoes; stir to break up tomatoes. Cover; bring to a boil. Reduce heat to medium-low; simmer 25 minutes. Stir in okra and plantain; simmer an additional 25 minutes. Stir in remaining 1 teaspoon mustard seeds and fresh cilantro.