Toast the pepitas in a dry pan over medium heat for about 2 minutes, moving them constantly, until they pop and smell nutty. Tip them out of the pan immediately.
Drain and rinse the black beans thoroughly under running water, then shake them dry.
Whisk the Greek yogurt with the lime juice, chopped chipotle and ground cumin to make the crema. Taste and adjust the chipotle before serving.
Chop the romaine and dice the tomato.
Build the bowls in layers: romaine, then beans, corn and tomato.
Spoon the crema over and finish with the cotija, toasted pepitas and cilantro. Do not toss.