Wash and dry all produce. Halve and peel onion; finely chop half and very thinly slice remaining. Core, deseed, and finely chop poblano. Roughly chop cilantro leaves and stems. Dice tomato. Quarter lime.

In a medium bowl, combine sliced onion, vinegar, 1 tsp sugar (2 tsp for 4 servings), a pinch of salt, and 1 TBSP water. Stir until sugar and salt are mostly dissolved. Set aside to marinate, stirring occasionally, until ready to serve.

Pat diced pork dry with paper towels. Heat a large drizzle of olive oil in a large pan over medium-high heat. Add pork; season with salt and pepper. Cook, stirring, until browned and cooked through, 4-5 minutes. Turn off heat. Using a slotted spoon, transfer to a plate. TIP: Carefully pour out any excess grease in pan.

Heat a large drizzle of olive oil in same pan over medium-high heat. Add chopped onion and poblano; season with salt and pepper. Cook, stirring, until softened, 3-4 minutes. Return pork to pan and add Fajita Spice, stock concentrate, half the tomato paste (all for 4 servings), and 1/4 cup water (1/3 cup for 4). Cook, stirring, until everything is coated and saucy, 1-2 minutes.

In a small bowl, combine sour cream, a squeeze of lime juice, and a pinch of salt and pepper. Stir in water 1 tsp at a time until mixture reaches a drizzling consistency. Meanwhile, wrap tortillas in damp paper towels and microwave until warm and pliable, about 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 remaining lime wedges on the side.