For individual stratas, butter insides of four individual baking dishes. If serving family style, butter inside of 8 inch baking dish.
In a bowl, whisk eggs with milk and Dijon. Season with salt and pepper to taste. Reserve.
Heat a heavy medium skillet over medium heat. Add the bacon and saute until crisp and golden, about 5 minutes. Using a slotted spoon, transfer the bacon to a bowl. Add the onion, green peppers, corn and scallions to the pan drippings in the same skillet and saute until translucent, about 4 minutes. Stir in the cooked bacon. Turn off the heat and set aside.
Fill the baking dish/es half way with cubed bread. Sprinkle with cheese over the bread, then top with vegetable mixture. Then one more layer of bread, vegetables, and finish it with cheese.
Pour egg mixture evenly over strata/s and let stand for minimum of 20 minutes or overnight.
Preheat the oven to 350 degrees F.
Bake strata/s uncovered until cooked through, puffed, and golden brown, about 30 minutes. Let stand 5 minutes before serving.
Garnish with avocado and cilantro, if using.