Heat oven to 400℉. Spray an 8 x 8-inch baking dish with cooking spray.
Cook the sausage in a large sauté pan over medium-high heat until browned, breaking up the sausage into small pieces as it cooks. Once the sausage is cooked through, transfer to a clean plate.
Add the onion, red pepper and zucchini to the same pan and sauté for 5 minutes until softened. Add the garlic and sauté for 1-2 minutes more, stirring occasionally, until fragrant.
Add in the salsa, beans, corn, cumin, cooked sausage, and stir until the mixture is completely combined. Remove pan from the heat, and set aside.
In a separate bowl, whisk together the eggs and milk until evenly combined.
Layer half of the tortillas in an even layer in the bottom of the 8 x 8 baking dish. Then top evenly with half of the sausage mixture, half of the egg mixture, and half of the cheese. Repeat with another layer of tortillas, sausage mixture, egg mixture and cheese.
Cover the dish with foil and bake for 45-50 minutes, or until the center of the casserole is cooked through and no longer jiggly.
Let the casserole cool for 10 minutes. Slice and serve warm. Serve with avocado, lime and cilantro.