Cut bread in 1-inch cubes. Place 12 cups lightly packed cubes in a single layer on a wire rack on a baking sheet and place on bottom rack in oven. Reserve any remaining bread for another use.
Cut pepper lengthwise into 1-inch strips, removing seeds and pulp. Place pepper strips, skin side up, on a different baking sheet and coat lightly with cooking spray. Place peppers on top rack in oven. Broil peppers and bread in oven at the same time, checking peppers every 30 seconds starting at 3 minutes. Remove peppers from oven when lightly browned. Remove bread cubes from oven.
Reduce oven to 375º.
Grate cheeses on the large holes of a box grater. Toss bread cubes with cheeses, onion and cilantro in a large mixing bowl.
Using a fine mesh strainer, strain the salsa, separating the liquid from the solids. Combine the drained solids from salsa, eggs, milk and cumin. Toss egg mixture with the bread mixture, making sure all bread cubes are saturated.
Coat a 13- x 9-inch baking dish with cooking spray. Spread bread mixture in dish and bake, uncovered, 35 to 40 minutes or until lightly browned and almost set in center.
While bread pudding is cooking, combine reserved liquid from salsa, sour cream, tomato paste and roasted red pepper strips in a blender and blend until smooth. Remove bread pudding from oven, cut into squares, and drizzle with sour cream sauce. Serve immediately.