Wash and dry all produce. Adjust rack to upper position and preheat oven to 475 degrees. Trim, then thinly slice scallions, separating greens and whites. Core and seed poblano, then cut into ½-inch pieces. Finely dice tomato. Thinly slice chili, removing ribs and seeds first for less heat. Drain beans over a small bowl, reserving liquid.

Heat a drizzle oil in a large pan over medium-high heat. Add poblano and cook until just softened, about 3 minutes. Meanwhile, set aside tsp ½ tsp Southwest spice in a small bowl.

Once poblano has cooked 3 minutes, add tomato, scallion whites, half the beans, 2 TBSP reserved bean liquid, and remaining Southwest spice to pan. 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, tossing, until beginning to soften, 2-3 minutes. Add 3 TBSP reserved bean liquid. Let simmer until warmed through, 1-2 minutes. Lower heat and stir in 1 TBSP butter. Remove pot from heat, then mash beans until mostly smooth with a potato masher or fork. 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 the filled side, and place seam-side down in an 8- by 11-inch baking dish or ovenproof pan. Spoon over enough salsa to generously coat. Sprinkle with cheese. Bake in oven until salsa is bubbly and cheese melts, 3-5 minutes.

Meanwhile, add sour cream to bowl with reserved ½ tsp Southwest spice. Stir in 1-2 tsp warm water, or enough to create a drizzly consistency. Season with salt and pepper. Drizzle baked enchiladas with crema. Garnish with scallion greens and chili, to taste. Divide between plates and serve.