How to Make It
Preheat oven to 350°F. Heat 2 tablespoons of the oil in a large skillet over medium-high. Add one-third of plantain strips, and fry until golden brown and slightly crispy, 2 to 3 minutes per side. Transfer to a paper towel-lined baking sheet. Repeat procedure 2 more times with 4 tablespoons of the oil and remaining plantain strips. Wipe skillet clean.
Stir together ground sirloin, onion, bell pepper, cilantro, garlic, sazón seasoning, adobo seasoning, and oregano in a large bowl until thoroughly combined. Heat remaining 1 tablespoon oil in skillet over medium-high; add ground sirloin mixture, and cook, stirring often, until beef is browned and vegetables are tender, 4 to 5 minutes. Stir in olives, tomato sauce, raisins, and bay leaves; bring mixture to a boil. Reduce heat to low, and simmer, stirring occasionally, 10 minutes. Remove from heat. Remove and discard bay leaves.
Grease a 9-inch square baking pan with butter. Layer one-third of plantain slices on bottom of pan. Top with half of sirloin mixture and 1 cup cheese. Repeat layers once. Top with remaining one-third of plantain slices.
Whisk together eggs and milk in a small bowl. Slowly pour egg mixture over casserole. Let stand 5 minutes. Sprinkle with remaining 1 cup cheese.
Bake in preheated oven until top is golden brown and mixture is bubbly, 25 to 30 minutes. Let stand 10 minutes before serving. Cut into 6 squares.