Evening before serving: Heat 2 tablespoons olive oil in a large skillet over medium heat. Add diced onion and bell peppers to skillet; sauté for 6-8 minutes until vegetables begin to soften. Add minced garlic to skillet and cook for 1 additional minute until fragrant. Add ground cumin, smoked paprika, dried oregano, and ground chipotle powder to skillet; stir constantly for 1 minute to bloom spices. Stir in roughly chopped spinach and diced green chiles; cook for approximately 2 minutes until spinach wilts completely. Remove skillet from heat and allow vegetable mixture to cool to room temperature (approximately 15 minutes). In a large mixing bowl, crack 12 large eggs and whisk vigorously for 2 minutes until completely homogeneous with no visible egg white streaks. Add ½ cup milk, ½ teaspoon salt, and ¼ teaspoon ground black pepper to whisked eggs; whisk again until completely incorporated. Lightly spray crockpot liner with cooking spray, paying special attention to corners and bottom to prevent sticking. Layer half of the cooled vegetable mixture on the bottom of the prepared crockpot. Sprinkle half of the combined grated cheeses over the vegetable layer (approximately 1½ cups total cheese). Pour the whisked egg mixture slowly and evenly over the cheese layer, allowing it to distribute throughout and fill gaps between vegetables. Layer the remaining cooled vegetables over the egg mixture. Top with remaining grated cheeses (approximately 1½ cups). Cover crockpot with lid and refrigerate overnight (or up to 24 hours maximum) before cooking. Morning of serving: Place covered crockpot on countertop for 15 minutes to bring to room temperature. Set crockpot to LOW temperature and cook covered for 6-7 hours (or set to HIGH and cook 3-4 hours, though LOW produces superior texture). Check doneness after 5 hours on LOW: gently shake crockpot—center should jiggle slightly like custard, not be completely firm. Insert a knife near center; it should come out nearly clean with minimal egg mixture on blade. Once cooked to desired doneness, turn off crockpot and remove lid. Allow casserole to rest covered for 10 minutes (carryover cooking continues to set the center without overcooking). Sprinkle fresh cilantro over top immediately before serving for maximum flavor and visual appeal. Serve directly from crockpot on LOW setting (if available) to maintain warmth throughout meal service. Accompany with fresh salsa, sour cream, guacamole, or additional cilantro as desired