Combine 1/2 packet of the fajita seasoning with 1/2 can of the beef consommé (or about 5 oz of beef broth). Marinate the steak for at least 30 minutes or up to four hours in the fajita seasoning/beef consommé mixture.
Heat 1/2 tablespoon of the vegetable oil in a non-stick skillet over medium high-heat. And preheat the oven to 275 degrees F.
Discard the marinade. Sear the steak on each side over medium-high heat, then transfer the skillet to the oven (with the steak) to finish cooking. Once the steak has reached at least 145 degrees F, remove it from the oven and keep covered until ready to serve.
In a separate, non-stick large skillet, heat the remaining vegetable oil and sauté the peppers and onions until starting to brown, then add the tomatoes, fajita and Tajin seasonings. Stir and simmer until the tomatoes have softened and burst. Remove the vegetables to a clean bowl.
In the same pan, melt the four tablespoons of butter, add the garlic and cook for about one minute, until fragrant. Whisk in the flour and tomato paste and cook for a couple of minutes, whisking often. Whisk in the beef consommé and cook, stirring until thickened. Reduce heat to low and stir in the sour cream until smooth.
Meanwhile, boil some water and cook the pasta to al dente. Drain and reserve about a cup of pasta water. Pour the cooked pasta into the pan with the sauce and stir until the pasta is completely coated. Add a little pasta water if necessary to loosen the sauce.
Thinly slice the steak against the grain. Top the cooked pasta with the vegetables and tender steak slices. Then sprinkle it with some fresh herbs, salt to taste and cracked black pepper to serve.