1 1- to 1 1/4-pound pork tenderloin, cut into 1/2-inch-thick medallions
3 tablespoons vegetable oil
1/2 onion, coarsely chopped
3/4 cup pumpkin seeds (pepitas)
1/4 cup peanuts (1 1/2 ounces)
1/4 cup sesame seeds (1 1/2 ounces)
2 garlic cloves, minced
4 cups water
12 ounces tomatillo,* husked
2 teaspoons coarsely chopped seeded jalapeño chili
1 1/2 cups fresh cilantro leaves
1 1/2 cups torn romaine leaves
1 1/4 cups low-salt chicken broth
3 radishes, trimmed, chopped
Heat 2 tablespoons oil in heavy large skillet over medium heat. Add next 5 ingredients. Sauté until seeds are lightly browned, about 4 minutes. Set aside.
Place 4 cups water, tomatillos, and jalapeño in small saucepan. Simmer over medium heat until tomatillos are soft and olive-green color, about 15 minutes. Drain, reserving 1/4 cup cooking liquid. Transfer tomatillos, jalapeño, reserved 1/4 cup liquid, cilantro, lettuce, broth, radishes, and seed mixture to blender. Blend sauce until smooth, stopping occasionally to push down ingredients.
Heat 1 tablespoon oil in large skillet over medium heat. Add sauce; cook until thickened, about 4 minutes. Season with salt and pepper. (Can be made 2 hours ahead. Let stand at room temperature.)
Prepare barbecue (medium-high heat). Sprinkle pork with salt and pepper. Grill until cooked through, about 2 minutes per side. Divide among 4 plates. Stir sauce over medium heat until heated through. Spoon sauce over pork.