Peel and chop the onion into ½ inch square pieces. Then seed and chop the bell peppers into ½ inch square pieces. Chop the cilantro and crumble the queso fresco. Juice one lime. Then cut the other lime into small wedges to use as a garnish.
Slice the flank steak into thin strips, against the grain. Then cut each strip into ¾ square pieces.
Place a large 14 inch cast iron skillet over high heat. Drizzle avocado oil in the skillet, then add in the flank steak. Sprinkle the steak with Mom’s Favorite Taco Seasoning. Cook for 1-2 minutes, stirring to brown the pieces on both sides. Then push the steak pieces to the side of the pan and add the onions and peppers to the middle. Sear the vegetables for 2-3 minutes, stirring occasionally.
Stir the steak and vegetables together. Pour the juice of one lime over the steak mixture. Add in 1/4 cup chopped cilantro and stir. Them turn off the heat.
Cut the avocados in half. Remove the pits. (Do this by tapping a sharp knife into the center of each pit, then twisting it. Knock the pit off the knife blade with the heel of your hand.) Use a spoon to scoop a large hole in the center of each avocado half, creating a deeper crater for the filling. Slice the avocado pieces you remove to use as a garnish.
Fill each avocado half with steak fajita filling. Place a few small pieces of sliced avocado on top. Then garnish the tops with queso fresco and cilantro. Serve with a lime wedge.