Adjust rack to top position and preheat oven to 475 degrees. Wash and dry all produce. Trim and thinly slice scallions, separating whites from greens. Core, deseed, and dice poblano. Finely dice tomato. Thinly slice chili. Drain beans over a small bowl, reserving liquid.

Heat a drizzle of oil in a large pan over medium-high heat. Add poblano and cook until just softened, 3-4 minutes.

Reserve ½ tsp Southwest Spice (1 tsp for 4 servings) in a second small bowl. Once poblano has cooked 3-4 minutes, add tomato, scallion whites, half the beans (you’ll use the rest later), 2 TBSP reserved bean liquid, and remaining Southwest Spice. Cook, stirring, until fragrant and warmed through, 2-3 minutes. Season with salt and pepper.

Heat a large drizzle of oil in a small pot over medium-high heat. Add remaining beans and cook, stirring, until slightly softened, 2-3 minutes. Add 3 TBSP reserved bean liquid (⅓ cup for 4 servings; you may have some left over). Simmer until warmed through, 1-2 minutes. Reduce heat to low and stir in 1 TBSP butter (2 TBSP for 4). Turn off heat; mash with a potato masher or fork until mostly smooth. Season with plenty of salt and pepper.

Spread tortillas with mashed beans. Place a small amount of filling on one half of each tortilla. Roll up tortillas, starting with filled side, and place seam sides down in an 8-by-11-inch baking dish or ovenproof pan. (For 4 servings, assemble in a 9-by-13-inch baking dish or two smaller ones.) Spoon enough salsa over to generously coat (you may have some left over). Sprinkle with Monterey Jack. Bake until salsa is bubbly and cheese has melted, 3-5 minutes.

Meanwhile, add sour cream to bowl with reserved Southwest Spice. Stir in warm water 1 tsp at a time until mixture reaches a drizzling consistency. Season with salt and pepper. Top baked enchiladas with crema, scallion greens, and as much chili as you like. Divide between plates and serve.