Add the blueberries, vinegar, lemon juice, honey and cayenne pepper to the bowl of a food processor. Blend until pureed.
Stream in the olive oil slowly while running the food processor until the dressing begins to come together and thicken slightly. Season with salt and pepper, to taste.
Set aside.
To make the salad:
Add the arugula, strawberry, blueberries, cucumber and red onions to a large bowl or platter.
Top the salad with the walnuts and goat cheese.
Drizzle the dressing over the salad and serve immediately.
Notes
Dressing can be made up to 3 days in advance. Store in the refrigerator in an airtight container. If the dressing thickens up when chilled, heat in the microwave for 15 seconds and stir before serving.