Awaken the Pepitas : Place the pepitas in a dry, medium skillet over medium heat. Toast for 3–5 minutes, shaking the pan frequently, until they are fragrant and make faint popping sounds. Immediately transfer them to a plate to cool to prevent burning.
Prepare the Greens : Gently separate, wash, and pat dry the butter lettuce leaves. Arrange 7–8 leaves on each of the four plates, creating a cup-like base for the salad.
Whisk the Vinaigrette : In a small bowl, whisk together the fresh lime juice, extra-virgin olive oil, and ground cumin until emulsified. Season lightly with a pinch of salt and a few grinds of black pepper.
Chop the Fresh Ingredients : On your cutting board, dice the mango into uniform ½-inch cubes. Thinly slice the scallion greens and give the cilantro a rough chop.
Assemble the Salad Base : In the large salad bowl, combine the coleslaw mix, drained black beans, diced mango, and sliced scallions.
Dress and Garnish : Drizzle the lime vinaigrette over the contents of the salad bowl. Toss gently until everything is lightly coated. Just before serving, fold in the cooled, toasted pepitas and the chopped cilantro to preserve their texture and freshness.
Plate for Serving : Spoon a generous portion of the finished salad mixture onto each prepared bed of butter lettuce. Serve immediately.