Preheat the oven to 400 degrees F. Line a baking sheet with foil for easy clean up.
Add the Brussels sprouts to the prepared baking sheet, drizzle with the olive oil and season with salt and pepper. Toss everything together. Roast the Brussels sprouts until tender, 30 to 35 minutes.
Add the arugula, apples, grapes and feta cheese to a large salad bowl. Add roasted Brussels sprouts and toss everything together. Drizzle with about 1/2 cup of the Simple Vinaigrette. Toss everything together.
Add the oil, vinegar, mustard and shallots to a jam jar and shake it up. Taste for seasoning and adjust as necessary with salt and pepper.