Prepare a medium-high (425°F to 450°F) gas or charcoal grill fire. Brush the portobellos on both sides with oil and season with salt and pepper.
Grill the portobellos gill side up until grill marks form on one side, about 3 minutes. Flip and continue to grill until tender, about 2 to 3 minutes more. Thinly slice the portobellos.
Put a tortilla in a 12-inch skillet over medium heat. Sprinkle the tortilla with half of the portobellos, scallions, and cheeses. Top with another tortilla and lightly press down with a metal spatula.
Cook, flipping once, until browned on both sides, 2 to 4 minutes per side. Transfer to a plate.
Repeat, using the remaining tortillas and filling. Slice the quesadillas into wedges and serve.
nutrition information (per serving):
35, Fat Calories
310, Saturated Fat
35, Monounsaturated Fat
89, Polyunsaturated Fat
Photo: Scott Phillips