Steak Fajitas with Green Sauce

Name: Steak Fajitas with Green Sauce
Ingredients: 1⁄4 cup fresh lemon juice; 1⁄4 cup pineapple juice; 1⁄4 cup sherry; 1⁄4 cup soy sauce; 3 tbsp. butter, melted; 1 tbsp. freshly ground black pepper; 3 whole dried chiles de árbol, crushed; 1 clove garlic, finely chopped; Zest of 2 lemons; Zest of 1 orange; 1 skirt steaks (about 3 lbs.), trimmed and halved crosswise; 6 tomatillos, husked and rinsed; 2 small serrano chiles, stemmed; 2 ripe avocados, such as Hass, Gwen, or Frey, peeled, seeded, and chopped; 1⁄2 cup sour cream; 1⁄4 cup chopped cilantro leaves; Salt; 6 tbsp. canola oil; 2 red bell peppers, cored, seeded, and thickly sliced; 2 yellow onions, thickly sliced; Warm flour tortillas