Lamb Stew with Sweet Potatoes

Ingredients

• 3 teaspoons olive oil
• 450 g well-trimmed lean leg of lamb, cut into 2.5-cm chunks
• 1 medium onion, finely chopped
• 4 cloves garlic, minced
• 1 cup canned crushed tomatoes
• 450 g sweet potatoes, peeled and cut into 1-cm chunks
• 2 tablespoons creamy peanut butter
• 1 teaspoon salt
• ½ teaspoon cayenne pepper
• 280 g frozen cut or whole okra, thawed