In a large skillet over a medium-high heat, combine the cooking fat with the garlic and onions. Cook for about 5 minutes, until the onions are soft and translucent in colour. Add the tilapia fillets to the skillet. Allow the fillets to cook for 3 to 4 minutes on one side prior to flipping. As the fish begins to cook through, use a fork to break it apart into flaky pieces. Add the jalapeno pepper, tomatoes, cilantro and lime juice to the mix and then season with salt and pepper to taste. Cook for 5 minutes before removing from heat. Serve the taco filling to your liking and garnish with fresh avocado slices.