Mix peanut oil, red pesto, paprika-mustard, soy sauce, and garlic-chili spice together in a shallow container with a whisk. Season beef fillet steaks lightly with sea salt and black pepper on both sides. Place steaks in the marinade, cover, and refrigerate for 3-4 hours. Remove from refrigerator and allow steaks to reach room temperature for 15-20 minutes before cooking.
Heat a coated grill pan to high heat. Sear the steaks for 2 minutes on each side (about 4 minutes total) until browned. Transfer steaks to a preheated 80°C (176°F) oven and rest for 30 minutes.