In a food processor, pulse three-fourths of the rice with the cheese, chipotle and 1 teaspoon of salt until slightly pasty. Add the poblano, scallions, peas and pumpkin seeds and pulse until the vegetables are coarsely chopped. Transfer the mixture to a bowl and knead in the remaining rice. Using moistened hands, form the mixture into four 4-inch patties, about 3/4 inch thick, pressing to compact.

Preheat a grill pan or nonstick skillet. Brush the burgers with oil and grill over moderate heat until golden and crusty, about 5 minutes. Carefully flip them and grill until heated through and golden, about 5 minutes longer. Stuff the burgers into the pitas with lettuce, tomato slices, sour cream and salsa.