• 2 1/2 to 3 pounds beef fillet
• 3/4 teaspoon sea salt
• 1/4 teaspoon freshly ground pepper
• 1 tablespoon extra-virgin olive oil

• 2 tablespoons sesame oil
• 2 small red onions , finely diced
• 5 cloves garlic , minced
• 1 small hot chile , halved with seeds discarded
• 5 tablespoons finely diced fresh ginger
• Bottom 3" stalk of   lemongrass , smashed with the flat side of a chef's knife
• 1 kaffir lime leaf , optional
• 2 cups French green lentils
• Sea salt and freshly ground pepper
• 3 tablespoons reduced-sodium soy sauce

• 1/2 cup rice vinegar
• 3 tablespoons granulated sugar
• 1 teaspoon coriander seeds
• 1 teaspoon yellow mustard seeds
• 1 small red onion , thinly sliced
• 1 stalk celery , thinly sliced
• 1/2 English cucumber , peeled and thinly sliced
• 4 to 5 radishes , thinly sliced
• 1/2 cup packed fresh mint leaves
• 1/2 cup packed fresh basil leaves , large leaves torn

• 1 large shallot , finely diced
• Zest of 4 limes and 3 tablespoons fresh lime juice
• 2 teaspoons light brown sugar
• 1/4 teaspoon minced hot chile
• 1 tablespoon grated fresh ginger
• 1 teaspoon fish sauce
• 1 teaspoon reduced-sodium soy sauce
• 4 cups packed baby Asian salad greens

To cook beef: Sprinkle beef with salt and pepper; let stand at room temperature for 30 minutes. Preheat oven to 400°. Heat olive oil in an ovenproof skillet over high heat. Add beef and sear, turning occasionally, until evenly browned, about 6 minutes. Place skillet with beef in oven and roast until medium-rare (about 15 minutes), which registers 135° on an instant-read thermometer. Set aside.

To make lentils: Warm the sesame oil in a large saucepan over medium heat. Add onions, garlic, chile, ginger, lemongrass, lime leaf (if using). Sauté 2 to 3 minutes. Stir in lentils and 1/2 teaspoon salt. Add 4 cups water and bring to a boil. Reduce heat and simmer until lentils are tender, 20 to 25 minutes. Drain liquid and discard chile, lemongrass, lime leaf. In a large bowl, combine lentils and soy sauce; season with salt and pepper. Cover and set aside.

To make relish: Combine vinegar, granulated sugar, coriander, mustard seeds in a small saucepan. Bring to a boil; reduce heat and simmer until reduced to a thin syrup, 5 to 6 minutes. Let cool. In a bowl, combine onion, celery, cucumber, radishes, mint, basil with enough syrup (about 3 tablespoons) to coat vegetables.

To make dressing: Combine shallot, lime zest, lime juice in a bowl; let stand 20 minutes. Stir in brown sugar, minced chile, ginger, fish sauce, soy sauce and 2 tablespoons water.

To serve: Spoon lentils onto a platter. In a large bowl, toss greens with 3 tablespoons of the dressing; arrange over the lentils. Slice beef; arrange over the greens. Spoon relish over the beef. Drizzle with remaining dressing.