Roasted Corn Tacos

1 to 2 tablespoons vegetable oil
1/2 medium white onion, thinly sliced
1 poblano chile, roasted, peeled and sliced into strips
2 ears corn, roasted, shucked and kernels removed
Salt to taste
4 ounces queso fresca, farmer's cheese, or ricotta
1 tablespoon chopped cilantro
Fresh corn tortillas

Heat the oil in a large saut