Wash and dry all produce. Halve and peel onion. Finely chop one half; very thinly slice other half from pole to pole. Core, seed, and dice poblano into 1/2-inch squares. Roughly chop cilantro. Core and dice tomato. Halve lime. Cut one half into wedges.

Place sliced onion, vinegar, 2 tsp sugar, 1/2 tsp salt, and 1 TBSP water in a medium bowl. Toss until sugar and salt are mostly dissolved. Set aside, tossing from time to time.

Heat a drizzle of olive oil in a large pan over medium-high heat. Add pork, breaking up meat into pieces. Season with salt and pepper. Cook, tossing, until browned, 4-5 minutes. Transfer to a plate and set aside.

Heat another drizzle of olive oil in same pan over medium-high heat. Add poblano and chopped onion. Season with salt and pepper. Cook, tossing, until softened, 3-4 minutes. Add pork to pan along with fajita spice, stock concentrate, 2 TBSP water, and 1 TBSP tomato paste (we sent more). Scrape up any browned bits on bottom. Cook, stirring, until thick and saucy, 2-3 minutes.

Combine sour cream, a squeeze of lime juice, and a pinch of chipotle powder (use more or less to taste) in a small bowl. Stir in enough water to give mixture a drizzling consistency, 1-2 tsp. Season with salt and pepper. Wrap tortillas in a damp paper towel and microwave on high until warm, about 30 seconds.

Divide filling, tomato, cheese, cilantro, pickled onion, and crema between tortillas. (TIP: You can put everything in individual serving bowls and let everyone assemble their own tacos.) Serve with lime wedges on the side for squeezing over.