Wash and dry all produce. Core, deseed, and thinly slice poblano. Finely dice tomato. Finely chop cilantro. Halve, peel, and thinly slice shallot. In a medium bowl, combine half the shallot, vinegar, 1 tsp sugar (1½ tsp for 4 servings), and salt. Let sit, stirring occasionally, until ready to serve.

In a small bowl, combine sour cream, half the Southwest Spice, and a large pinch of salt. Stir in water, 1 tsp at a time, until mixture reaches a drizzling consistency.

Heat a drizzle of oil in a large pan over medium-high heat. Add poblano and cook, stirring, until slightly softened, 3-4 minutes. Stir in remaining shallot and a large pinch of salt and pepper. Cook, stirring, until lightly browned and softened, 2-3 minutes. Turn off heat; transfer to a second medium bowl. Wipe out pan.

Pat steak dry with paper towels. Heat another drizzle of oil in same pan over high heat. Add steak and season with salt, pepper, and remaining Southwest Spice. Cook, stirring occasionally, until browned and cooked through, 2-3 minutes. Return veggies to pan; stir until combined. Turn off heat.

Wrap tortillas in damp paper towels and microwave until warm, about 30 seconds. (Alternatively, wrap tortillas in foil and warm in oven at 425 degrees for 5 minutes.) Stir tomato into bowl with pickled shallot.

Divide steak mixture between tortillas. Top with salsa, crema, and cilantro. Serve.