Preheat oven to 425 degrees. Place the squash halves cut side up on a baking sheet and brush with olive oil. Bake for 30 minutes or until the squash is easily pierced with a fork; let cool.
Meanwhile, melt the butter in a saucepan over medium heat. Add the garlic cook for 1 minute or until fragrant.
Add sliced sage leaves and sliced shallots and cook for 1-2 minutes. Pour shallot, garlic, sage butter in a bowl and set aside.
Preheat the broiler. Lightly brush both sides of the bread slices with the garlic, shallot butter. Keep the remaining butter.
Place the bread slices on a baking sheet broil for 1-2 minutes or until golden brown, turning once.
Once the baked squash has cooled scrape out the pulp with a fork into a food processor or blender and pulse until smooth.
Add the remaining garlic, shallot butter, lemon juice, zest, and season with salt and pepper. Blend until smooth.
Spread the squash butter on the crostini and top with ricotta cheese. Top with equal slices of prosciutto and sprinkle with pomegranate seeds.