Whisk together jam, juice and two vinegars in a bowl.

Add oil and whisk to combine.

Add salt and pepper to taste.

Melt butter in a non-stick skillet over medium heat.

Add sugar and pepper; stir to blend.

Add nuts and stir until nuts are coated. Transfer to a plate and cool. (These can be done in advance and stored in an airtight container until needed.)

Arrange watermelon slices around the edge of a large platter.

Toss greens with vinaigrette to coat and place in the center.

Top with nuts and onion slices.