Heat oven to 425°F (220°C). Line a light colored sheet pan with parchment paper.
Toss sweet potatoes with olive oil until combined. Season with salt and pepper. Place sweet potatoes on prepared sheet pan. Bake for 30 - 35 minutes, flipping halfway through the cooking process, until softened and golden brown.
Meanwhile add olive oil, water, dates, apple cider vinegar, rosemary, mustard, salt, and pepper to a food processor. Pulse on high until fully combined, scraping down the sides as needed, until no whole pieces of rosemary or dates remain.
Toss together mixed greens, half of the cooked sweet poatoes, half of the pomegranate seeds, half of the pepitas, half of the apples, and dressing in a serving bowl. Top with the remaining sweet potatoes, pomegranate seeds, pepitas, apples, and the prosciutto in a line on the top of the salad. Serve immediately.