Wash and dry produce. Dice tomato into ½-inch pieces. Trim and thinly slice scallions, separating whites from greens. Quarter lime. Halve, peel, and thinly slice onion. Halve, core, and thinly slice green bell pepper into strips.

In a small bowl, combine tomato, scallion greens, and juice from half the lime. Season with salt and pepper. In a separate small bowl, combine 3 TBSP sour cream (or 6 TBSP for 4 servings) and a pinch of Southwest Spice Blend (you'll use the rest in the next step). Add water 1 tsp at a time until mixture reaches a drizzling consistency.

Pat 10 oz (20 oz for 4 servings) steak dry with paper towels; thinly slice against the grain. Season all over with remaining Southwest Spice Blend, salt, and pepper.

Heat a drizzle of cooking oil in a large pan over medium-high heat. Add steak, onion, bell pepper, and scallion whites. Cook, stirring occasionally, until veggies are tender and steak is cooked to desired doneness, 3-6 minutes.

Wrap flour tortillas in damp paper towels; microwave until warm and pliable, about 30 seconds.

Divide tortillas between plates; fill with steak and fajita veggies. Top with ½ cup Monterey Jack (1 cup for 4 servings), pico de gallo (draining first), and spiced crema. Serve with remaining lime wedges on the side.