In a medium bowl, whisk together the soy sauce, olive oil, lemon juice, and keto Worcestershire sauce until well combined. The oil and acidic components need proper emulsification to coat the meat evenly. Add the minced garlic, Dijon mustard, onion powder, salt, pepper, and dried rosemary, stirring until all ingredients are fully incorporated and the garlic is evenly distributed throughout the liquid.

Place your steak in a container or resealable bag that fits snugly—I prefer bags because they use less marinade and allow better contact with the meat. Pour the marinade from Step 1 over the steak, making sure it's fully submerged or well-coated on all sides. Cover and refrigerate for 1 to 12 hours depending on your schedule; even 1 hour will add flavor, but longer marinating times (4-8 hours) will deepen the taste more effectively.

Remove the steak from the refrigerator 15-20 minutes before cooking to bring it closer to room temperature for even cooking. Take the steak out of the marinade, letting excess liquid drip back into the container, then cook using your preferred method—pan-searing over high heat, grilling, or broiling all work beautifully with this marinade. Discard the used marinade and any remaining liquid after cooking.