Position racks in the upper and lower thirds of the oven; preheat to 425 degrees F. Line a baking sheet with foil and coat with cooking spray. Combine the cornflakes, 1 tablespoon olive oil and the paprika in a medium bowl; season with salt and pepper. Combine the yogurt, lemon juice, 1 tablespoon water, 1/4 teaspoon salt and a few grinds of pepper in a large bowl; add the chicken and toss to coat.
Dredge the chicken in the cornflake mixture, pressing to help it adhere. Transfer to the prepared baking sheet; mist with cooking spray. Bake on the upper oven rack until lightly browned, about 15 minutes. Flip the chicken and bake until cooked through, 7 to 10 more minutes.
Meanwhile, toss the green beans, garlic, scallion whites and the remaining 1 tablespoon olive oil in a bowl; season with salt and pepper. Spread on another baking sheet; bake on the lower oven rack, stirring occasionally, until tender, about 20 minutes. Toss with the lemon zest and scallion greens. Serve with the chicken and honey mustard.