Place the sliced sirloin steak in a sealable bag and add the soy sauce and pineapple juice. Shake to mix, then press out the excess air, seal, and refrigerate for 8 hours or overnight.
Preheat oven to 400 degrees F.
In a large, oven-proof skillet, heat 1 tbsp avocado oil over medium-high heat.
Remove the steak from the marinade and thoroughly pat dry with paper towels. When the pan is up to temp, add the steak to the skillet and sear for 1-2 minutes on each side to achieve a golden brown crust. Then continue cooking another 2-4 minutes, stirring often, until your desired doneness. Transfer the steak to a plate, tent with foil, and let it rest while you cook the vegetables.
Reduce the heat to medium and add the remaining 2 tbsp of oil to the pan. Add the sliced peppers and onion. Cook, stirring often, for 2-3 minutes. Add the fajita seasoning, and cook 3-4 minutes more until crisp-tender.
Add the drained diced tomatoes and green chilies, lime juice, and cooked rice. Cook for 1-2 more minutes, stirring occasionally. Turn off the heat, add the steak back to the pan, stir, then sprinkle the cheese over the top.
Bake for 3-5 minutes until the cheese has melted. Serve with your favorite fajita toppings.