Preheat the broiler. Finely crush the cornflakes in a resealable plastic bag using your hands. Transfer to a bowl and toss with 1 tablespoon olive oil, the lemon zest, chopped thyme, 1/2 teaspoon salt and a few grinds of pepper; set aside. Cut the corn kernels off the cob. Run the back of a knife down the cobs to remove any corn milk; reserve separately from the kernels.
Heat 1 tablespoon olive oil in a large ovenproof skillet over medium-high heat. Add the zucchini, season with 1/4 teaspoon salt and cook, stirring occasionally, until softened and beginning to brown, 2 to 3 minutes. Add the remaining 1 tablespoon olive oil, the corn kernels, tomatoes, garlic, thyme sprigs and 1/4 teaspoon salt; cook, stirring occasionally, until the corn and garlic are tender, 1 to 2 minutes.
Stir in the cream and corn milk and bring to a simmer. Reduce the heat to maintain a gentle simmer and cook until slightly thickened, about 3 minutes. Season with salt and pepper. Remove from the heat and stir in the chicken, then stir in the cheese until melted and creamy. Sprinkle with the cornflake mixture. Broil until golden, 1 to 3 minutes. Let cool slightly before serving.