Preheat oven to 400°F. Place tomatoes and tomatillos on rimmed baking sheet sprayed with nonstick cooking spray. Drizzle with oil; sprinkle with salt. Roast in 400°F oven 25 to 30 minutes or until juices have evaporated and skins are blistered; set aside.
Meanwhile, cut 32 rounds from tortillas with 2-1/2-inch diameter cookie cutter; set aside. Combine cheeses in small bowl; set aside.
Heat pot roast in microwave oven according to package directions; cool slightly. Remove from gravy; discard gravy or reserve for another use. Shred pot roast with two forks; set aside.
Place 16 tortillas rounds on rimmed baking sheet sprayed with nonstick cooking spray. Top each evenly with cheese mixture and shredded beef. Cover with remaining tortilla rounds. Spray tortilla tops with nonstick cooking spray. Bake in 400°F oven about 10 minutes or until cheese is melted and tortillas are lightly browned, turning halfway through cooking time.
Top each quesadilla with 1 tomatillo slice, yellow tomato slice and cherry tomato half. Serve immediately.
Nutrition information per serving: 134 Calories; 63 kcal Calories from fat; 7 g Total Fat; 2 g Saturated Fat; 2 g Monounsaturated Fat; 14 mg Cholesterol; 524 mg Sodium; 13 g Total Carbohydrate; 2 g Dietary Fiber; 6 g Protein; 0.9 mg Iron; 0.5 mg NE Niacin; 0 mg Vitamin B6; 0 mcg Vitamin B12; 0.2 mg Zinc; 0.7 mcg Selenium;