Preheat grill to high heat (450° to 500°). Cut peppers in half lengthwise; discard seeds and membranes. Grill 4 minutes on each side or until blackened. Place in a zip-top plastic bag; let stand 15 minutes. Peel away charred skins, and chop. Set aside.
Combine oil and seasoning blend; brush onto both sides of vegetables, and sprinkle with salt. Reduce heat to medium-high (350° to 400°), and grill vegetables 4 to 6 minutes on each side or until tender. Transfer to a large bowl; set aside until cool enough to handle. Cut vegetables into bite-size pieces. Stir in chopped peppers.
Top each of 4 tortillas with one-fourth vegetable mixture; divide cheeses evenly over vegetables. Place remaining tortillas over cheese, pressing down gently.
Grill quesadillas over medium heat (300° to 350°) for 2 minutes. Quickly and carefully turn quesadillas, using a large, wide spatula. Grill, covered with grill lid, 2 more minutes or until cheese melts and tortillas are golden. Cut each quesadilla into 6 wedges, and serve immediately with salsa.