Pat the flank steak dry and season both sides with sea salt, black pepper, and garlic powder.
Heat avocado oil in a cast-iron skillet over high heat and sear the steak for 3-4 minutes per side until medium-rare.
Remove steak from heat, let it rest for 5 minutes, then slice into small, bite-sized cubes.
Bring a small pot of water to a boil, add the shrimp, and cook for 2 minutes until opaque and pink.
Immediately transfer shrimp to an ice bath to stop the cooking, then pat dry and chop into halves.
In a large glass bowl, whisk together the lime juice and lemon juice, then stir in the diced red onion, chopped cilantro, and minced jalapeño.
Add the cubed steak and shrimp to the bowl, tossing thoroughly to ensure every piece is submerged in the citrus marinade.
Cover and refrigerate for 15 minutes, then gently fold in the diced avocado before serving in chilled bowls.