Adjust rack to middle position (middle and top positions for 4 servings) and preheat oven to 425 degrees. Wash and dry produce.

Drain polenta and transfer to a large bowl; using your hands, crumble into pea-size pieces.

Add flour, half the Southwest Spice Blend, half the mozzarella, 2 TBSP water, and ¼ tsp salt (4 TBSP water and ½ tsp salt for 4). Using your hands, mash until flour and cheese are thoroughly incorporated, 30-60 seconds. Set dough aside to rest for 10 minutes.

While dough rests, finely dice jalapeño, removing ribs and seeds for less heat. Trim and thinly slice scallions, separating whites from greens. Zest and quarter lime. Finely chop cilantro. Finely dice tomato.

In a small microwave-safe bowl, combine vinegar, 2 TBSP water, 1 tsp sugar, and a pinch of salt (4 TBSP water and 2 tsp sugar for 4 servings). Stir in jalapeño and scallion whites. Microwave until dark green, 30 seconds. Set aside to pickle, stirring occasionally, until ready to use in Step 7.

In a separate small bowl, combine lime zest, half the cilantro, half the garlic powder (you’ll use the rest later), 2 TBSP olive oil (4 TBSP for 4), and juice from half the lime. Season with salt and pepper to taste.

In a third small bowl, combine sour cream, juice from remaining lime, and a pinch of salt.

Divide dough into four equal portions (eight portions for 4 servings); shape each into a ball. On a clean work surface, flatten each ball into a ¼-inch-thick round using the palm of your hand. TIP: If dough feels sticky, spray your work surface and hands with nonstick cooking spray.

While arepas cook, pat steak* dry with paper towels. Season all over with remaining Southwest Spice Blend, salt, and pepper.

Heat a large drizzle of oil in a second large pan over medium-high heat. Add steak to pan and sear until browned all over, 3-4 minutes.

Bake steak and arepas on middle rack until arepas are cooked through and steak is cooked to desired doneness, 12-15 minutes. (For 4 servings, transfer steaks to a second sheet; roast steak on top rack and arepas on middle rack, swapping rack positions halfway through.)

Remove sheet from oven. Sprinkle remaining mozzarella over each arepa. Return to middle rack and bake until cheese melts, 1 minute. Transfer steak to a cutting board to rest. 

Using a slotted spoon, transfer jalapeño mixture to a fourth small bowl. Add tomato, remaining cilantro, and remaining garlic powder; stir to combine. Season with salt and pepper to taste.

Slice steak against the grain.

Divide steak and arepas between plates. Top arepas with guacamole, ají salsa, and a drizzle of crema. Top steak with chimichurri. Serve.