Heat 1 tablespoon olive oil in a large pan over medium-high heat. Add steak; cook until browned, 4 to 5 minutes per side. Transfer steak to a cutting board and let rest, about 5 minutes. Slice into thin strips.
Slice courgettes, carrot and radishes into ribbons using a spiraliser.
Heat remaining 2 tablespoons oil in the pan over medium heat. Add carrot ribbons; cook and stir until lightly browned, about 3 minutes. Add courgette ribbons; cook, stirring constantly, until tender, about 5 minutes.
Divide carrot and squash noodle mixture between 2 serving plates. Top with sliced steak. Garnish with radish noodles, avocado, grape tomatoes and coriander.
Whisk soured cream and sriracha sauce together in a small bowl. Drizzle over serving plates.