Prepare the vinaigrette: Combine olive oil, apple cider vinegar, basil, brown sugar, Dijon mustard, garlic, and fresh raspberries in a bowl of a food processor . Season with salt and pepper, to taste. Pulse until smooth.
Prepare the salad: Put the spinach in a large serving bowl and top with the raspberries, blueberries, red onions, feta, and almonds. Drizzle with the vinaigrette. Serve immediately.