Thinly slice the Beef Sirloin across the grain into bite-sized strips and toss them with a generous pinch of Salt, freshly ground Black Pepper and about a tablespoon of Berbere to coat; let rest while you prepare the aromatics.
Heat a large heavy skillet over medium-high heat and add 1 tablespoon Neutral Oil. When the oil shimmers, stir in a spoonful of Niter Kibbeh until it melts and becomes fragrant.
Add the sliced Onion, minced Garlic, and chopped Jalapeño to the pan and sauté until the onion is softened and translucent, 3–4 minutes; toss in a few chopped sprigs of Rosemary and cook another minute to release the herb oils.
Stir in the diced Tomato and cook until it breaks down slightly and the mixture looks saucy, about 3 minutes.
Increase the heat to high, add the seasoned beef in a single layer and let it sear without moving for 1–2 minutes, then toss and continue to cook until just browned and cooked through, about 2–3 more minutes depending on thickness.
Deglaze the pan with a splash (about 2 tablespoons) of Tej and a few tablespoons of Water if needed, scraping up any browned bits; let the liquid reduce until it forms a glossy pan sauce that clings to the meat.
Taste and adjust seasoning with more Salt or Berbere if desired, then finish by squeezing in Lemon Juice and adding a few wedges or thin slices of Lemon for brightness.
Serve the Zilzil Tibs immediately, spooned onto warm Injera or alongside it so guests can soak up the spicy, buttery sauce.
