Preheat the oven to 400°F. Set out a large baking sheet, lining it with parchment paper if you like.
Make the hemp seed ranch dressing. In a blender, combine the hemp seeds, lemon juice, water, olive oil, dijon, garlic powder, nutritional yeast, salt, and pepper. Whizz the mixture on high until you have a smooth and creamy texture. Scrape the dressing into a small bowl and stir in the green onions and dill. Cover the dressing and store in the refrigerator.
Place the diced sweet potatoes onto one end of the baking sheet. Toss the sweet potatoes with 1 teaspoon of the olive oil, some salt and pepper. Slide the sheet into the oven and set your timer for 15 minutes.
At the 15 minute mark, remove the baking sheet. In a small bowl, toss the tempeh pieces with another teaspoon of olive oil, some salt and pepper. Arrange the tempeh pieces in the middle segment of the baking sheet. Lightly toss the sweet potatoes. Slide the sheet back into the oven and set your timer for another 15 minutes.
At the 15 minute mark, remove the baking sheet. Throw the brussels sprouts into the same small bowl that you used for the tempeh. Toss the brussels sprouts with the remaining olive oil, salt, and pepper. Scatter them in a single layer on the remaining segment of the baking sheet.
Flip the tempeh pieces over and brush them with the barbecue sauce. Slide the sheet back into the oven for 15 more minutes. Once brussels sprouts are lightly browned, remove baking sheet from the oven.
Transfer sweet potatoes, tempeh, and brussels sprouts to a serving bowl. Drizzle some of the hemp seed ranch dressing over top and enjoy.