Marinate beef: Peel and finely chop 1½ teaspoons garlic. Squeeze 1 tablespoon lime juice into a medium bowl. Cut any remaining lime into wedges. Add 2½ teaspoons of the taco seasoning, 1 teaspoon of the chopped garlic, 1 tablespoon oil, and a pinch each of salt and pepper to lime juice, stirring to combine. Add beef strips and toss to coat. Set aside to marinate until step 4.

Prep salad, make dressing: Halve romaine lengthwise, then cut crosswise into very thin slices, discarding end. Roughly chop cilantro leaves and tender stems together. In a medium bowl, whisk together remaining chopped garlic, 2 tablespoons oil, and 1 tablespoon vinegar. Season to taste with salt and pepper.

Warm tortillas: Heat a medium nonstick skillet over medium-high. Add 1 tortilla at a time, and cook until warmed and lightly golden, about 30 seconds per side. Transfer to a plate and wrap in foil to keep warm. Repeat with remaining tortillas. (Alternatively, toast tortillas over a gas flame until lightly charred in spots, 5–10 seconds per side.)

Cook beef: Heat 1 tablespoon oil in same skillet over high. Using a slotted spoon, add beef to skillet and cook, without stirring, until browned on the bottom, 2–3 minutes. Reduce heat to medium, then add marinade and cook, stirring, until beef is cooked through, 1–2 minutes.

Dress salad: Add pepitas, romaine, and half of the cilantro to bowl with dressing. Toss to combine, then season to taste with salt and pepper.

Assemble tacos & serve: Fill tortillas with beef, then top with salsa, sour cream, and remaining cilantro. Serve with romaine salad alongside. Pass any lime wedges for squeezing.