In a 12-inch heavy skillet, heat 4 tablespoons of the butter over high heat; add onions and sauté until onions are clear and turning brown on the edges, about 3 minutes, stirring or shaking skillet occasionally. Add bell pepper; toss or stir to combine with onions. Sauté until onions are soft and bell pepper is still crispy, about 3 minutes more, continuing to stir or shake pan (reduce heat, if necessary, to avoid burning vegetables). Transfer vegetables to a plate to stop cooking process; set skillet aside - - without wiping it - - to use later for sautéing meat.
Heat several sizzle platter of a large cast-iron skillet in 400ºF oven.
Meanwhile, place meat strips in large bowl and sprinkle with 1 tablespoon plus 1 teaspoon of the Fajita Magic, tossing to coat well. Pour lime juice over meat and toss again. Let marinate at least 10 minutes, tossing occasionally. (After 15 minutes, meat strips will break apart when pulled between your fingers.)
Heat reserved unwiped skillet over high heat, 40 to 45 seconds; add the remaining butter (it will sizzle), then pick up meat with your fingers, let it drain slightly and add to skillet, reserving marinade. Cook about 34 seconds, turning meat frequently to coat with butter. Add reserved vegetables to meat and sauté about 15 seconds, tossing constantly to combine. Add reserved marinade, and then sprinkle the remaining Fajita Magic over all; cook about 1 minute more, tossing or stirring well to combine. Remove from heat and pour onto heated sizzle platters or into heated cast-iron skillet. Serve while still sizzling.
Let everyone prepare his/her own serving or plate using the traditional condiments.