Adjust rack to middle position and preheat oven to 425 degrees. Wash and dry all produce. Halve poblanos lengthwise; remove ribs and seeds. Dice tomato. Trim and thinly slice scallions, separating whites from greens. Zest and quarter lime (quarter both limes for 4 servings).

In a small pot, combine 1 cup water (2 cups for 4 servings), stock concentrate, and a large pinch of salt. Bring to a boil, then add quinoa, cover, and reduce heat to low. Simmer until quinoa is tender and water has evaporated, 15-20 minutes. TIP: Drain any excess water, if necessary.

While quinoa cooks, rub poblano halves with oil; season with salt and pepper. Place cut sides down on a baking sheet. Roast on middle rack until tender, 18-20 minutes. Meanwhile, in a small bowl, combine sour cream, lime zest, and a squeeze of lime juice. Add water 1 tsp at a time until mixture reaches a drizzling consistency. Season with salt and pepper.

Drain corn and pat dry with paper towels. Heat a drizzle of oil in a large, preferably ovenproof, pan over high heat. Add corn and cook, stirring occasionally, until lightly charred, 4-6 minutes. (TIP: If corn begins to pop, cover pan.) Reduce heat to medium and add tomato, scallion whites, and Southwest Spice. Cook, stirring occasionally, until tomato breaks down, 2-3 minutes. Season with salt and pepper. Turn off heat.

Stir cooked quinoa into pan with veggies; season with salt and pepper. Once poblanos are done roasting, stuff each half with as much grain mixture as will fit. Place in pan with remaining grain mixture, nestling each poblano half into the grains. (TIP: If your pan isn't ovenproof, transfer mixture to a small baking dish and arrange stuffed poblanos in there.) Sprinkle evenly with cheese. Heat broiler to high or oven to 500 degrees.

Transfer pan with stuffed poblanos to middle rack; broil or bake until cheese is melted and lightly browned, 2-3 minutes. Remove from oven and top with lime crema and scallion greens. Divide between plates. Serve with any remaining lime wedges on the side.