- For the dressing, add the dill, parsley, scallions, thyme, and mayonnaise to a blender or food processor and process for 1 minute. With the motor running, slowly add the buttermilk and process until the dressing is smooth and creamy. Add the vinegar, salt, hot sauce, and black pepper and process for 30 seconds. You should have about 1 1/2 cups of dressing. Place the dressing in a container, cover, and refrigerate.
- Preheat an oven broiler or set an outdoor grill to high heat. Cover a broiler tray with foil, and coat it with nonstick cooking spray (or coat the grill rack with cooking spray). With a sharp knife, make three diagonal slashes spaced several inches apart on one side of the flank steak. This will prevent the steak from curling while cooking. Place the steak on the broiler pan or directly on the grill about 4 to 5 inches from the heat source. Cook for 11 to 12 minutes for medium, turning once. Cook longer to your liking. Remove the steak from the grill, put it on a plate, and tent it with foil to keep warm.
- Combine the mixed greens, red pepper, red onion, cherry tomatoes, and basil in a large bowl. Set aside.
- Add the pumpkin seeds to a small dry skillet. Toast the seeds over medium heat for 3 to 4 minutes, shaking the pan occasionally until lightly browned. Watch carefully so they don't burn. Set aside.
- Thinly slice the flank steak. Add 2 Tbsp. of the dressing to the salad green mixture and toss well. Divide the salad among 6 plates. Top with the sliced steak. Drizzle with an additional 1 Tbsp. of dressing per serving. Garnish with pumpkin seeds.
Note: You will have leftover dressing for another use. Store in an airtight container and use within 1 week.