Preheat broiler to high. Place poblano and bell peppers on a baking sheet lined with 2 long sheets of foil. Place pan on top rack of oven; broil 12 minutes or until blackened and charred, turning after 6 minutes. Remove from oven; loosely wrap peppers in foil, crimping edges to seal. Cool. Working on foil, peel and seed peppers. Transfer to a cutting board; discard skin, seeds, membranes, and foil. Cut peppers into 1/2-inch-wide strips. Preheat oven to 400°F. Combine onion, oil, pumpkin, potato, and garlic; toss. Sprinkle with flour and next 4 ingredients (through ground red pepper), tossing to coat. Place one-third of pumpkin mixture in a 13- x 9-inch baking dish coated with cooking spray. Sprinkle with one-third of pepper strips. Repeat procedure twice with pumpkin mixture and peppers. Pour milk over vegetables. Coat top layer with cooking spray. Cover with foil; bake at 400°F for 45 minutes. Uncover and sprinkle with cheese. Bake an additional 10 minutes or until potatoes and pumpkin are tender.