Fresh salsa and portobello mushrooms elevate this meal from basic to gourmet.
Heat grill to medium. In a small bowl, whisk together oil and vinegar; season with salt and pepper. Brush both sides of mushrooms with oil mixture; starting with stem side up, grill mushrooms until tender when pierced with the tip of a sharp paring knife, 8 to 12 minutes, turning once. Remove from grill; slice 1/2 inch thick.
Layer one half of each tortilla with cheese, scallions, mushroom slices, and then more cheese, dividing toppings evenly. Fold tortilla over filling; using your hands, carefully transfer filled tortilla to grill. Cook until tortilla is slightly charred and cheese is melted, 2 to 3 minutes per side. Serve with salsa, and garnish with sour cream, if desired.