Preheat oven to 350° F. Toss walnuts with 1 tablespoon maple syrup in small bowl. Arrange in a single layer on parchment-lined baking sheet and bake for 5 to 10 minutes, until syrup is bubbling. Remove from oven and cool.
In small bowl or dish, combine remaining maple syrup, raspberry balsamic vinegar, kosher salt and white pepper. Slowly, while whisking, pour in extra virgin olive oil until incorporated.
To serve, toss butter lettuce, strawberries, green onions, feta cheese and walnuts together. Dress with vinaigrette. Remaining dressing can be stored in refrigerator.
Note: If you can't find raspberry balsamic vinegar, make your own by combining 1 tablespoon raspberry preserves with enough balsamic vinegar to make 1/4 cup.