For the tomatillo salsa: Preheat the oven to 425 degrees F. Combine the tomatillos, garlic and onion on a baking sheet. Toss with the canola oil and some salt and pepper to combine. Roast in the oven until the mixture is slightly charred and soft, stirring once, about 30 minutes. Remove from the oven and let cool slightly. Reduce the oven heat to 375 degrees F.
Transfer the mixture to a food processor and process until coarsely chopped. Add the spinach, cilantro, chipotle, lime juice and some salt and pepper and process until smooth. Taste, and add some honey as desired to balance the acidity of the tomatillos. Measure out 1 cup and transfer the rest to a serving bowl.
For the strata: Butter a 9-by-13-inch baking dish. Whisk the eggs in a medium bowl until smooth. Add the milk, 1 cup of the tomatillo salsa, half of the Cheddar, half of the Monterey Jack and the cilantro and stir until combined. Stir in the chips and let the mixture sit for 15 minutes. Scatter the remaining Cheddar and Monterey Jack on top.
Transfer the mixture to the prepared baking dish and bake until lightly golden brown and puffed, about 30 minutes. Remove from the oven, top with the cotija and bake for another 5 minutes.
While the strata bakes, make the salad: Heat the canola oil in a medium skillet over medium heat. Add the corn and cook, tossing, just to warm, about 30 seconds. Add the tomatoes, avocados, parsley and some salt and pepper and toss gently once or twice.
Combine the green onions, lime juice, mustard and some salt and pepper in a bowl. Whisk in about 1/3 cup olive oil to combine; taste, add more oil or honey as desired.
Pour the green onion vinaigrette around the corn mixture and fold gently to combine. Let the salad sit at room temperature for about 15 minutes before serving.
Let the casserole sit for 10 minutes before serving. Serve with the tomato-corn-avocado salad and the remaining tomatillo salsa.