Wash and dry all produce. Halve and peel onion; very thinly slice one half and finely chop other half. Core, deseed, and dice poblano into 1/2-inch pieces. Roughly chop cilantro. Dice tomato. Halve lime; cut one half into wedges.

In a medium bowl, combine sliced onion, vinegar, 2 tsp sugar, 1/2 tsp salt, and 1 TBSP water. Stir until sugar and salt are mostly dissolved. Set aside, stirring occasionally, until ready to serve.

Heat a drizzle of olive oil in a large pan over medium-high heat. Add pork and season with salt and pepper. Cook, breaking up meat into pieces, until browned and cooked through, 4-6 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, stirring, until softened, 3-4 minutes. Return pork to pan along with Fajita Spice, stock concentrate, half the tomato paste (use all for 4 servings), and 1/4 cup water (1/3 cup for 4). Cook, scraping up any browned bits from bottom of pan, until mixture is thickened and saucy, 1-2 minutes.

In a small bowl, combine sour cream, a squeeze of juice from lime half to taste, and a pinch of chipotle powder (add more to taste if you like things spicy). Stir in water 1 tsp at a time until mixture reaches a drizzling consistency. Season with salt and pepper. Wrap tortillas in damp paper towels and microwave until warm and pliable, 30 seconds.

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