Preheat your oven to 400°F and line a large baking sheet with parchment paper.
Place the broccoli florets on one side of the baking sheet, drizzle with olive oil, and sprinkle with half of the sea salt and black pepper. Toss to coat evenly.
Crush the cornflakes into a coarse meal using a sealed bag or a mortar and pestle, then transfer them to a shallow bowl.
In a small mixing bowl, whisk together the first 2 tablespoons of Greek yogurt, garlic powder, onion powder, and the remaining salt and pepper.
Pat the chicken tenderloins dry, then coat each one thoroughly in the yogurt mixture before rolling in the crushed cornflakes to create an even crust.
Place the coated chicken tenderloins on the other side of the baking sheet next to the broccoli.
Bake for 15 to 18 minutes, or until the chicken is golden and cooked through and the broccoli is tender with slightly charred edges.
While everything roasts, prepare the dipping sauce by whisking the remaining 2 tablespoons of Greek yogurt with the minced garlic clove and lemon juice in a small ramekin.
Serve the crispy chicken tenderloins and roasted broccoli immediately with the garlic yogurt sauce on the side.