Preheat oven to 450 degrees F. Season filet mignon steaks generously with salt and pepper. In a heavy, ovenproof skillet, heat olive oil over medium-high heat until almost smoking. Pan-sear the steaks, only on 1 side, for 2 minutes until a crust forms. Transfer the pan to the oven and roast for 10 minutes or until cooked medium rare.
To prepare the salsa: Toss together the tomatillo, jicama, avocado, red onion and grape tomatoes. Pour half the chimichurri sauce into the salsa and toss gently to coat. Serve the steaks, crust side up, with salsa and remaining chimichurri.
To prepare the Chimichurri: Combine garlic, jalapeno and lime in a small bowl. Whisk in vinegar and olive oil. Stir in parsley and cilantro. Add salt, cover and let stand 2 hours to allow the flavors to marry.