Set an oven rack about 6 inches from the heat source and preheat the oven's broiler. Line a baking sheet with aluminum foil. Place peppers with cut sides down onto the prepared baking sheet.

Cook under the preheated broiler until the skin of the peppers has blackened and blistered, 5 to 8 minutes. Place blackened peppers into a bowl and cover tightly with plastic wrap. Allow peppers to steam as they cool, about 15 minutes.

Meanwhile, preheat the oven to 350 degrees F (175 degrees C). Spray a 9x13-inch baking dish with cooking spray and line the bottom with bread slices.

Cook chorizo over medium-high heat until starting to brown, about 3 minutes. Transfer to a bowl. Heat oil in the same pan. Add onion; cook and stir until tender, about 3 minutes. Peel poblanos and slice flesh. Mix with the onion.

Beat eggs and milk together in a large bowl. Season with garlic powder, salt, and pepper.

Spread chorizo over the bread slices. Cover with onion-poblano mixture. Pour the beaten eggs on top. Sprinkle cheese blend over the top.

Bake in the preheated oven until eggs are set and top is starting to brown, about 30 minutes.