Heat the olive oil in a large non-stick skillet over medium high. Add sweet potatoes, brussels sprouts, plant-based sausage, and onion. Season with salt and black pepper. Cook for 10 minutes, stirring occasionally, or until the vegetables are crisp-tender and the onions become translucent.
Mix in the apples, garlic, rosemary, and cinnamon (optional). Sauté for 30 seconds, then pour in the vegetable broth and liquid smoke. Bring to a boil and cook until evaporated, about 2 minutes. Serve warm.