To prepare a chimichurri cauliflower steaks with mashed sweet potatoes recipe, you'll first need to prepare the cauliflower. Cut off the ends of the stalks of cauliflower and remove the stems from the florets. Scoop out the insides and cut them into 1/4-inch thick slices. Heat the olive oil in the skillet over medium-high heat. Add the chopped red onion and cook until softened, about 5 minutes. Stir in 2 tablespoons each chopped garlic and thyme. Cook, stirring frequently, until the onion is translucent and the garlic begins to turn golden brown, 2 to 3 minutes more. Remove the pan from heat and add the sweet potato puree. Season with salt and pepper and toss to combine.