Pre-heat the oven to 375 degrees.
Place the squash on a large baking sheet. Drizzle with 1½ teaspoons of olive oil and sprinkle with the ground cinnamon and a good pinch of kosher salt. Toss to combine, then arrange the squash in an even layer, making sure to leave a little bit of space between each cube. Roast for 25-30 minutes, stirring once halfway through the cooking time, until the squash is very tender. Remove from the oven and let cool slightly.
Meanwhile, prep the Brussels sprouts. Slice the sprouts in half lengthwise, and then slice them very thinly crosswise. Heat 1 teaspoon of olive oil in a medium skillet over medium-high heat. When the oil is hot and shimmering, add the sprouts in an even layer and cook, undisturbed, for 2-3 minutes so that they get a nice little char on the bottom. Add a pinch of salt and a little pepper (if you like) and cook for another 1-2 minutes, stirring periodically, just until tender. Stir in the lemon juice and cook for 1 minute more. Transfer the sprouts to a bowl and set aside.
Next, prep the crostini. Pre-heat the broiler on high. Arrange the baguette slices on a large baking sheet. Lightly brush both sides of each slice with the remaining 2 tablespoons of olive oil and sprinkle with a little salt. Place the bread under the broiler for 1-2 minutes on each side until lightly brown. (Pay close attention here, it is scarily easy to burn crostini.) Remove from the broiler and briefly set aside.
Transfer the cooked squash to the bowl of a food processor (or high-speed blender). Add the ricotta and process until very smooth. Taste and season with salt and pepper. (You can also add a ¼ teaspoon pure maple syrup here if you have a sweet tooth.)
Time to assemble the crostini! Spread each crostini with a generous dollop of butternut squash puree, then top with some shaved Brussels sprouts and a few pomegranate arils. Transfer to a serving plate or platter and serve.