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 finely chop poblano. Roughly chop cilantro. Core and dice tomatoes. Halve lime; cut one half into wedges for serving.

Add sliced onion, vinegar, 2 tsp sugar, 1/2 tsp salt, and 1 TBSP water to a medium bowl. Toss until sugar and salt are mostly dissolved. Set aside to marinate, tossing occasionally.

Heat a large 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 until browned, 4-5 minutes. Transfer to a plate using a slotted spoon. Pour out and discard any excess grease in pan.

Heat another large drizzle of olive oil in same pan over medium-high heat. Add chopped onion and poblano. Season with salt and pepper. Cook, tossing, until softened, 3-4 minutes. Return pork to pan and add fajita spice, 2 TBSP tomato paste (we sent more), stock concentrate, and 2 TBSP water. Cook, stirring, until everything comes together in a saucy mixture, 2-3 minutes.

Combine sour cream, a squeeze of lime juice, and a pinch of salt and pepper in a small bowl. Stir in a splash or two of water to give crema a drizzly consistency. Meanwhile, wrap tortillas in a damp paper towel and microwave on high until warm, about 30 seconds.

Divide filling, tomatoes, 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.