Preheat oven to 350°F (175°C). This takes about 10 minutes. Lightly grease a 9x13-inch baking dish with butter or cooking spray. Set aside. Checkpoint: Oven is preheated and dish is ready when you can hold your hand 3 inches above the rack and feel strong heat.

In a large mixing bowl, combine 2 cups cottage cheese, 1 cup ricotta cheese, 1 cup shredded cheddar cheese, and 3 large eggs. Stir for about 2 minutes with a wooden spoon or whisk until the mixture is smooth and creamy with no lumps visible. Checkpoint: The cheese base should look uniform and creamy, with no cottage cheese curds visible.

Add 2 minced garlic cloves, 1/2 teaspoon dried Italian seasoning, 1/2 teaspoon salt, 1/4 teaspoon black pepper, and 1/4 teaspoon red pepper flakes to the cheese mixture. Stir well for about 1 minute until the seasonings are evenly distributed throughout. Checkpoint: The mixture should smell fragrant and aromatic; no streaks of seasoning should be visible.

Prepare vegetables while the cheese base is resting: dice 1 medium zucchini into 1/4-inch pieces (about 1 cup), dice 1 medium bell pepper into small pieces (about 3/4 cup), chop 1 cup broccoli florets into bite-sized pieces (about 1/2 inch each), dice 1 cup carrots into small cubes (about 1/4 inch), dice 1/2 cup onion into small pieces, roughly chop 1 cup fresh spinach, and dice 1/2 cup mushrooms into small pieces. This prep takes about 10-15 minutes.

Fold all prepared vegetables into the cheese mixture using a rubber spatula. Work gently for about 2 minutes, scraping from the bottom of the bowl upward to ensure vegetables are evenly distributed. Some vegetables may break slightly, which is fine. Checkpoint: No large pockets of vegetables should be visible; they should be scattered throughout the cheese base.

Pour the entire vegetable and cheese mixture into the prepared 9x13-inch baking dish. Use a spatula to spread the mixture evenly, pressing gently so it fills the dish in one even layer. Checkpoint: The surface should be relatively flat and level across the entire dish.

In a small bowl, combine 1/2 cup panko breadcrumbs with 2 tablespoons melted butter. Mix for about 30 seconds with a fork until the breadcrumbs are evenly coated and no dry spots remain. Add 1 cup shredded cheddar cheese, 1 tablespoon grated Parmesan cheese, and 2 tablespoons fresh chopped parsley. Toss together for another 30 seconds until evenly combined. Checkpoint: The topping should be crumbly, moist, and golden-colored with herbs visible.

Sprinkle the breadcrumb topping evenly over the vegetable casserole, spreading it across the entire surface with your fingers or a spoon. Press down gently so the topping adheres but doesn't compress into a solid layer. Checkpoint: You should see a visible, crumbly golden layer covering the casserole with some texture variation visible on top.

Place the baking dish on the center rack of the preheated 350°F oven. Bake uncovered for 45-50 minutes. The casserole is done when: (1) the top is golden brown to deep golden (not pale), (2) the edges are bubbling slightly (you may see light juices at the edges), and (3) a knife inserted into the center comes out clean (not wet or doughy). Checkpoint: Top should be deeply golden brown, edges may show light bubbling, and the center should not jiggle when you gently shake the dish.

Remove from oven using oven mitts. The dish will be very hot. Place on a heat-safe surface or trivet and let rest at room temperature for 5 minutes. This allows the casserole to set and cool slightly, making it easier to cut and serve. Checkpoint: The casserole should feel firm to the touch on top (though still hot), and you should be able to hold your hand 6 inches above it without feeling intense heat.

Cut into squares (approximately 8 pieces) and serve warm. Use a spatula to remove each piece, keeping the golden topping intact if possible. Serves 4-6 people depending on portion size.